First, industry has made credible arguments that their resources are
stretched to the limit developing and testing strategies for compliance
with the 2007/2010 heavy-duty highway emissions standards. We do not
want to jeopardize their success toward that goal by being too
aggressive with our OBD program. Second, OBD is a complex and difficult
regulation with which to comply. We believe that our implementation
schedule would give industry the opportunity to introduce OBD systems
on a limited number of engines giving them and us very valuable
learning experience. Should mistakes or errors in regulatory
interpretation occur, the ramifications would be limited to only a
subset of the new vehicle fleet rather than the entire new vehicle
fleet. Lastly, the proposed OBD requirements outlined above, and the
production vehicle evaluation provisions discussed in Section VIII,
reflect 10 to 20 years of learning by EPA, CARB, and industry
(primarily the light-duty gasoline industry) as to what works and what
does not work. This is, perhaps, especially true for those OBD elements
that involve the interface between the OBD system and service and I/M
inspection personnel. Gasoline manufacturers have had the ability to
evolve their OBD systems along with this learning process. However,
diesel engine manufacturers have not really been involved in this
learning process and, as a result, 100 percent implementation in 2010
would be analogous to implementing 10 to 20 years of OBD learning in
one implementation step. We believe that implementing in two or three
gradual steps rather than one big step will benefit everyone involved.
    Table II.G-1 makes reference to ``parent'' and ``child'' ratings.
In general, engine manufacturers certify an engine family that consists
of several ratings having slightly different horsepower and/or torque
characteristics but no differences large enough to require a different
engine family designation. For emissions certification, the parent
rating--i.e., the rating for which emissions data are submitted to EPA
for the purpose of demonstrating emissions compliance--is defined as
the ``worst case'' rating. This worst case rating is the rating
considered as having the worst emissions performance and, therefore,
its compliance demonstrates that all other ratings within the family
must comply. For OBD purposes, we wanted to limit the burden on
industry--hence the proposal for only one compliant engine family in
2010--yet maximize the impact of the OBD system. Therefore, for model
years 2010 through 2012, we are defining the OBD parent rating as the
rating having the highest weighted projected sales within the engine
family having the highest weighted projected sales, with sales being
weighted by the useful life of the engine rating. Table II.G-2 presents
a hypothetical example for how this would work. Using this approach,
the OBD compliant engine family in 2010 would be the engine family
projected to produce the most in-use emissions (based on sales weighted
by expected miles driven). Likewise, the fully liable parent OBD rating
would be the rating within that family projected to produce the most
in-use emissions.

                             Table II.G-2.--Hypothetical Example of How the OBD Parent and Child Ratings Would Be Determined
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                OBD weighting--    OBD weighting--
                                                                                Projected       Certified    engine rating \a\  engine family \b\
                  OBD group                          Engine family         Rating        sales        useful life       (billions)         (billions)

--------------------------------------------------------------------------------------------------------------------------------------------------------
I............................................  A                                 1          10,000         285,000              2.85              14.25
                                               ........................          2          40,000         285,000             11.4    .................
                                               B                                 1          10,000         435,000              4.35              21.60
                                               ........................          2          20,000         435,000              8.70   .................
                                               ........................          3          30,000         285,000              8.55   .................
II...........................................  C                                 1          20,000         110,000              2.20               7.70
                                               ........................          2          50,000         110,000              5.50   .................
--------------------------------------------------------------------------------------------------------------------------------------------------------
Notes: (a) For engine family A, rating 1, 10,000 x 285,000 / 1 billion = 2.85.
(b) For engine family A, 2.85 + 11.4 = 14.25.

    In the example shown in Table II.G-2, the compliant engine family
in 2010 would be engine family B and the parent OBD rating within that
family would be rating 2. The other OBD compliant ratings within engine
family B would be dubbed the ``child'' ratings. For model years 2013
through 2015, the parent ratings would be those ratings having the
highest weighted projected sales within each of the one to three engine
families having the highest weighted projected sales, with sales being
weighted by the useful life of the engine rating. In the example shown
in Table II.G-2, the parent ratings would be rating 2 of engine family
A, rating 2 of engine family B, and rating 2 of engine family C (Note
that this is only for illustration purposes since our proposal would
not require that a manufacturer with only three engine families have
three parent ratings and instead would require only one).
    The manufacturer would not need to submit test data demonstrating
compliance with the emissions thresholds for the child ratings. We
would fully expect these child ratings to use OBD calibrations--i.e.,
malfunction trigger points--that are identical or nearly so to those
used on the parent rating. However, we would allow manufacturers to
revise the calibrations on their child ratings where necessary so as to
avoid unnecessary or inappropriate MIL illumination. Such revisions to
OBD calibrations have been termed ``extrapolated'' OBD calibrations
and/or systems. The revisions to the calibrations on child ratings and
the rationale for them would need to be very clearly described in the
certification documentation.
    For the 2013 and later model years, we are proposing that
manufacturers certify one to three parent ratings. The actual number of
parent ratings would depend upon the manufacturer's fleet and would be
based on both the emissions control system architectures present in
their fleet and the similarities/differences of the engine families in
their fleet. For example, a manufacturer that uses a DPF with
NOX adsorber on each of the engines would have only one
system architecture. Another manufacturer that uses a DPF with
NOX adsorber on some engines and a DPF with SCR on others
would have at least two architectures. We would expect that
manufacturers would group similar architectures and similar engine

families into so called ``OBD groups.'' These OBD groups would consist
of a combination of engines, engine families, or engine ratings that
use the same OBD strategies and similar calibrations. The manufacturer
would be required to submit details regarding their OBD groups as part
of their certification documentation that shows the engine families and
engine ratings within each OBD group for the coming model year. While a
manufacturer may end up with more than three OBD groups, we do not
intend to require a parent rating for more than three OBD groups.
Therefore, in the example shown in Table II.G-2, rather than submitting
test data for the three parent ratings as suggested above, the OBD
grouping would result in the parent ratings being rating 2 of engine
family B and rating 2 of engine family C. These parents would represent
OBD groups I and II, and the manufacturer's product line. For 2013
through 2015, we intend to allow the 2010 parent to again act as a
parent rating and, provided no significant changes had been made to the
engine or its emissions control system, complete carryover would be
possible. However, for model years 2016 and beyond, we would work
closely with CARB staff and the manufacturer to determine the parent
ratings so that the same ratings are not acting as the parents every
year. In other words, our definitions for the OBD parent ratings as
discussed here apply only during the years 2010 through 2012 and again
for the years 2013 through 2015. We request comment on this approach.
    In addition to this gradual certification implementation schedule,
we are proposing some relaxations for in-use liability during the 2010
through 2018 model years. The first such relaxation is higher interim
in-use compliance standards for those OBD monitors calibrated to
specific emissions thresholds. For the 2010 through 2015 model years,
an OBD monitor on an in-use engine would not be considered non-
compliant (i.e., subject to enforcement action) unless emissions
exceeded twice the OBD threshold without detection of a malfunction.
For example, for an EGR monitor on an engine with a NOX FEL
of 0.2 g/bhp-hr and an OBD threshold of 0.5 g/bhp-hr (i.e., the
NOX FEL+0.3), a manufacturer would not be subject to
enforcement action unless emissions exceeded 1.0 g/bhp-hr
NOX without a malfunction being detected. For the model
years 2016 through 2018, parent ratings would be liable to the
certification emissions thresholds, but child ratings and other ratings
would remain liable to twice the certification thresholds. Beginning in
the 2019 model year, all families and all ratings would be liable to
the certification thresholds.
    The second in-use relaxation is a limitation in the number of
engines that would be liable for in-use compliance with the OBD
emissions thresholds. For 2010 through 2012, we are proposing that
manufacturers be fully liable in-use to twice the thresholds for only
the OBD parent rating. The child ratings within the compliant engine
family would have liability for monitoring in the manner described in
the certification documentation, but would not have liability for
detecting a malfunction at the specified emissions thresholds. For
example, a child rating's DPF monitor designed to operate under
conditions X, Y, and Z and calibrated to detect a backpressure within
the range A to B would be expected to do exactly that during in-use
operation. However, if the tailpipe emissions of the child engine were
to exceed the applicable OBD in-use thresholds (i.e., 2x the
certification thresholds during 2010-2015), despite having a
backpressure within range A to B under conditions X, Y, and Z, there
would be no in-use OBD failure nor cause for enforcement action. In
fact, we would expect the OBD monitor to determine that the DPF was
functioning properly since its backpressure was in the acceptable
range. For model years 2013 through 2015, this same in-use relaxation
would apply to those engine families that do not lie within an engine
family for which a parent rating has been certified. For 2016 and later
model years, all engines would have some in-use liability to
thresholds, either the certification thresholds or twice those
thresholds.
    These in-use relaxations are meant to provide ample time for
manufacturers to gain experience without an excessive level of risk for
mistakes. They would also allow manufacturers to fine-tune their
calibration techniques over a six to ten year period.
    We are also proposing some a specific implementation schedule for
the standardization requirements discussed in section II.F. We
initially intended to require that any compliant OBD engine family
would be required to implement all of the standardization requirements.
However, we became concerned that, during model years 2010 through
2012, we could have a situation where OBD compliant engines from
manufacturer A might be competing against non-OBD engines from
manufacturer B for sales in the same truck. In such a case, the truck
builder would be placed in a difficult position of needing to design
their truck to accommodate OBD compliant engines--along with a
standardized MIL, a specific diagnostic connector location
specification, etc.--and non-OBD engines. After consideration of this
almost certain outcome, we have decided to limit the standardization
requirements that must be met during the 2010 through 2012 model years.
Beginning in 2013, all engines will be OBD compliant and this would
become a moot issue. Table II.G-3 shows the proposed implementation
schedule for standardization requirements.

  Table II.G-3.--OBD Standardization Requirements for Diesel Fueled and
               Gasoline Fueled Engines Over 14,000 Pounds
------------------------------------------------------------------------
                                          Required           Waived
    Model year        Applicability    standardization   standardization
                                          features          features
------------------------------------------------------------------------
2010-2012.........  Parent and Child  Emissions         Standardized
                     ratings within    related           connector
                     1 compliant       (II.F.4) except   (II.F.2).
                     engine family.    for the           Dedicated
                     \a\               requirement to    (i.e.,
                                       make the data     regulated OBD-
                                       available in a    only) MIL.
                                       standardized      Communication
                                       format or in      protocols
                                       accordance with   (II.F.3).
                                       SAE J1979/1939    Emissions
                                       specifications)   related
                                       . MIL             functions
                                       activation and    (II.F.4) with
                                       deactivation.\b   respect to the
                                       \ Performance     requirement to
                                       tracking--calcu   make the data
                                       lation of         available in a
                                       numerators,       standardized
                                       denominators,     format or in
                                       ratios.           accordance with
                                                         SAE J1979/1939
                                                         specifications)
                    Other engine      None............  All.
                     families.
2013+.............  All engine        All.............  None.
                     families and
                     ratings.
------------------------------------------------------------------------
Notes: (a) Parent and child ratings are defined in section II.G; which
  rating serves as the parent rating and which engine families must
  comply is not left to the manufacturer, as discussed in section II.G.
  (b) There would be no requirement for a dedicated MIL and no
  requirement to use a specific MIL symbol, only that a MIL be used and
  that it use the proposed activation/deactivation logic.

2. In-Use Enforcement
    When conducting our in-use enforcement investigations into OBD
systems, we intend to use all tools we have available to analyze the
effectiveness and compliance of the system. These tools may include on-
vehicle emission testing systems such as the portable emissions
measurement systems (PEMS). We would also use scan tools and data
loggers to analyze the data stream information to compare real world
operation to the documentation provided at certification.
    Importantly, we would not intend to pursue enforcement action
against a manufacturer for not detecting a failure mode that could not
have been reasonably predicted or otherwise detected using monitoring
methods known at the time of certification. For example, we are
proposing a challenging set of requirements for monitoring of DPF
systems. As of today, engine manufacturers are reasonably confident in
their ability to detect certain DPF failure modes at or near the
proposed thresholds--e.g., a leaking DPF resulting from a cracked
substrate--but are not confident in their ability to detect some other
DPF failure modes--e.g., a leaking DPF resulting from a partially
melted substrate. If a partially melted substrate indeed cannot be
detected and this is known during the certification process, we cannot
expect such a failure to be detected on an in-use vehicle.
    We also want to make it clear who would be the responsible party
should we pursue any in-use enforcement action with respect to OBD. We
are very familiar with the heavy-duty industry and its tendency toward
separate engine and component suppliers. This contrasts with the light-
duty industry which tends toward a more vertically integrated
structure. The non-vertically integrated nature of the heavy-duty
industry can present unique difficulties for OBD implementation and for
OBD enforcement. With the complexity of OBD systems, especially those
meeting the requirements being proposed today, we would expect the
interactions between the various parties involved--engine manufacturer,
transmission manufacturer, vehicle manufacturer, etc.--to be further
complicated. Nonetheless, in the end the vast majority of the proposed
OBD requirements would apply directly to the engine and its associated
emission controls, and the engine manufacturer would have complete
responsibility to ensure that the OBD system performs properly in-use.
Given the central role the engine and engine control unit would play in
the OBD system, we are proposing that the party certifying the engine
and OBD system (typically, the engine manufacturer) be the responsible
party for in-use compliance and enforcement actions. In this role, the
certifying party would be our sole point of contact for potential
noncompliances identified during in-use or enforcement testing. We
would leave it to the engine manufacturer to determine the ultimate
party responsible for the potential noncompliance (e.g., the engine
manufacturer, the vehicle manufacturer, or some other supplier). In
cases where remedial action such as an engine recall would be required,
the certifying party would take on the responsibility of arranging to
bring the engines or OBD systems back into compliance. Given that
heavy-duty engines are already subject to various emission requirements
including engine emission standards, labels, and certification, engine
manufacturers currently impose restrictions via signed agreements with
engine purchasers to ensure that their engines do not deviate from
their certified configuration when installed. We would expect the OBD
system's installation to be part of such agreements in the future.

H. Proposed Changes to the Existing 8,500 to 14,000 Pound Diesel OBD
Requirements

    We are also proposing changes to our OBD requirements for diesel
engines used in heavy-duty vehicles under 14,000 pounds (see 40 CFR
86.005-17 for engine-based requirements and 40 CFR 86.1806-05 for
vehicle or chassis-based requirements). Table II.H-1 summarizes the
proposed changes to under 14,000 pound heavy-duty diesel emissions
thresholds at which point a component or system has failed to the point
of requiring an illuminated MIL and a stored DTC. Table II.H-2
summarizes the proposed changes for diesel engines used in heavy-duty
applications under 14,000 pounds. The proposed changes are meant to
maintain consistency with the diesel OBD requirements we are proposing
for over 14,000 pound applications.

 Table II.H-1.--Proposed New, or Proposed Changes to Existing, Emissions Thresholds for Diesel Fueled CI Heavy-
                                    duty Vehicles Under 14,000 Pounds (g/mi)
----------------------------------------------------------------------------------------------------------------
      Component/monitor              MY             NMHC             CO              NOX               PM
----------------------------------------------------------------------------------------------------------------
NMHC catalyst system.........  2010-2012.....  2.5x.
                               2013+.........  2x.
NOX catalyst system..........  2007-2009.....  ..............  ..............  3x............
                               2010+.........  ..............  ..............  +0.3.
DPF system...................  2010-2012.....  2.5x..........  ..............  ..............  4x.
                               2013+.........  2x............  ..............  ..............  +0.04.
Air-fuel ratio sensors         2007-2009.....  2.5x..........  2.5x..........  3x............  4x.
 upstream.
                               2010-2012.....  2.5x..........  2.5x..........  +0.3..........  +0.02.
                               2013+.........  2x............  2x............  +0.3..........  +0.02.
Air-fuel ratio sensors         2007-2009.....  2.5x..........  ..............  3x............  4x.
 downstream.
                               2010-2012.....  2.5x..........  ..............  +0.3..........  4x.
                               2013+.........  2x............  ..............  +0.3..........  +0.04.
NOX sensors..................  2007-2009.....  ..............  ..............  4x............  5x.
                               2010-2012.....  ..............  ..............  +0.3..........  4x.
                               2013+.........  ..............  ..............  +0.3..........  +0.04.
``Other monitors'' with        2007-2009.....  2.5x..........  2.5x..........  3x............  4x.
 emissions thresholds.
                               2010-2012.....  2.5x..........  2.5x..........  +0.3..........  4x.
                               2013+.........  2x............  2x............  +0.3..........  +0.02.
----------------------------------------------------------------------------------------------------------------
Notes: MY=Model Year; 2.5x means a multiple of 2.5 times the applicable emissions standard; +0.3 means the
  standard plus 0.3; not all proposed monitors have emissions thresholds but instead rely on functionality and
  rationality checks as described in section II.D.4.

Table II.H-2.--Proposed New, or Proposed Changes to Existing, Emissions Thresholds for Diesel Fueled CI Engines Used in Heavy-duty Vehicles Under 14,000
                                                                    Pounds (g/bhp-hr)
--------------------------------------------------------------------------------------------------------------------------------------------------------
        Component/Monitor                  MY                Std/FEL              NMHC                CO                NOX                  PM
--------------------------------------------------------------------------------------------------------------------------------------------------------
NMHC catalyst system.............  2010-2012.........  All...............  2.5x.
                                   2013+.............  All...............  2x.
NOX catalyst system..............  2007-2009.........  >0.5 NOX..........  .................  .................  1.75x.
                                   2007-2009.........  < =0.5 NOX.........  .................  .................  +0.5.
                                   2010+.............  All...............  .................  .................  +0.3.
DPF system.......................  2010-2012.........  All...............  2.5x.............  .................  .................  0.05/+0.04.
                                   2013+.............  All...............  2x...............  .................  .................  0.05/+0.04.
Air-fuel ratio sensors upstream..  2007-2009.........  >0.5 NOX..........  2.5x.............  2.5x.............  1.75x............  0.05/+0.04.
                                   2007-2009.........  < =0.5 NOX.........  2.5x.............  2.5x.............  +0.5.............  0.05/+0.04.
                                   2010-2012.........  All...............  2.5x.............  2.5x.............  +0.3.............  0.03/+0.02.
                                   2013+.............  All...............  2x...............  2x...............  +0.3.............  0.03/+0.02.
Air-fuel ratio sensors downstream  2007-2009.........  >0.5 NOX..........  2.5x.............  .................  1.75x............  0.05/+0.04.
                                   2007-2009.........  < =0.5 NOX.........  2.5x.............  .................  +0.5.............  0.05/+0.04.
                                   2010-2012.........  All...............  2.5x.............  .................  +0.3.............  0.05/+0.04.
                                   2013+.............  All...............  2x...............  .................  +0.3.............  0.05/+0.04.
NOX sensors......................  2007-2009.........  >0.5 NOX..........  .................  .................  1.75x............  0.05/+0.04.
                                   2007-2009.........  < =0.5 NOX.........  .................  .................  +0.5.............  0.05/+0.04.
                                   2010+.............  All...............  .................  .................  +0.3.............  0.05/+0.04.
``Other monitors'' with emissions  2007-2009.........  >0.5 NOX..........  2.5x.............  2.5x.............  1.75x............  0.05/+0.04.
 thresholds.
                                   2007-2009.........  < =0.5 NOX.........  2.5x.............  2.5x.............  +0.5.............  0.05/+0.04.
                                   2010-2012.........  All...............  2.5x.............  2.5x.............  +0.3.............  0.03/+0.02.
                                   2013+.............  All...............  2x...............  2x...............  +0.3.............  0.03/+0.02.
--------------------------------------------------------------------------------------------------------------------------------------------------------
Notes: MY=Model Year; 2.5x means a multiple of 2.5 times the applicable emissions standard or family emissions limit (FEL); +0.3 means the standard or
  FEL plus 0.3; 0.05/+0.04 means an absolute level of 0.05 or an additive level of the standard or FEL plus 0.04, whichever level is higher; not all
  proposed monitors have emissions thresholds but instead rely on functionality and rationality checks as described in section II.D.4.

1. Selective Catalytic Reduction and Lean NOX Catalyst
Monitoring
    We are proposing that the 8,500 to 14,000 pound SCR and lean
NOX catalyst monitoring requirements mirror those discussed
in section II.B.6. The current regulations require detection of a
NOX catalyst malfunction before emissions exceed 1.5x the
emissions standards. We no longer believe that such a tight threshold
level is appropriate for diesel SCR and lean NOX catalyst
systems. We believe that such a tight threshold could result in too
many false failure indications. The required monitoring conditions with
respect to performance tracking (discussed in section II.B.6.c) would
not apply for under 14,000 pound heavy-duty applications since we do
not have performance tracking requirements for under 14,000 pound
applications. We are proposing this change for the 2007 model year.
2. NOX Adsorber System Monitoring
    We are proposing that the 8,500 to 14,000 pound NOX
adsorber monitoring requirements mirror those discussed in section
II.B.7. The current regulations require detection of a NOX
adsorber malfunction before emissions exceed 1.5x the emissions
standards. We no longer believe that such a tight threshold level is
appropriate for diesel NOX adsorber systems. We believe that
such a tight threshold could result in too many false failure
indications. The required monitoring conditions with respect to
performance tracking (discussed in section II.B.7.c) would not apply
for under 14,000 pound heavy-duty applications since we do not have
performance tracking requirements for under 14,000 pound applications.
We are proposing this change for the 2007 model year.
3. Diesel Particulate Filter System Monitoring
    We are proposing that the 8,500 to 14,000 pound DPF monitoring
requirements mirror those discussed in section II.B.8. Our current
regulations require detection of a catastrophic failure only. The
proposed monitoring requirements discussed in section II.B.8 would be
far more comprehensive and protective of the environment than would a
catastrophic failure monitor. The required monitoring conditions with
respect to performance tracking (discussed in section II.B.8.c) would
not apply for under 14,000 pound heavy-duty applications since we do
not have performance tracking requirements for under 14,000 pound
applications. We are proposing no changes to the DPF monitoring
requirements in the 2007 to 2009 model years because there is not
sufficient lead time for manufacturers to develop a new monitor. The
new, more stringent monitoring requirements would begin in the 2010
model year, with a further tightening of the DPF NMHC threshold in the
2013 model year as is also proposed for over 14,000 pound applications.
4. NMHC Converting Catalyst Monitoring
    We are proposing that the 8,500 to 14,000 pound NMHC converting
catalyst monitoring requirements mirror those discussed in section
II.B.5. Our current regulations do not require the monitoring of NMHC
catalysts on diesel applications. The proposed monitoring requirements
discussed in section II.B.5 would be far more comprehensive and
protective of the environment than the current lack of any requirement.
The required monitoring conditions with respect to performance tracking
(discussed in section II.B.8.c) would not apply for under 14,000 pound
heavy-duty applications since we do not have performance tracking
requirements for under 14,000 pound applications. We are not proposing
this new threshold for the 2007 to 2009 model years because there is
not sufficient lead time for manufacturers to develop a new monitor.
The new, more stringent monitoring requirements would begin in the 2010
model year, with a further tightening of the NMHC threshold in the 2013
model year as is also proposed for over 14,000 pound applications.
5. Other Monitors
    We are also proposing changes to the emissions thresholds for all
other diesel monitors in the 8,500 to 14,000 pound range (e.g.,
NOX sensors, air fuel ratio

sensors, etc.). These proposed changes are meant to maintain
consistency with the proposed changes for over 14,000 pound
applications. We believe that these proposed thresholds are far more
appropriate for diesel applications than the thresholds we have in our
current OBD requirements which are, generally, 1.5 times the applicable
standards. None of the proposed thresholds represents a new threshold
where none currently exists. Instead, they represent different
thresholds that would require, in most cases, malfunction detection at
different emissions levels than would be required by our current OBD
requirements.
6. CARB OBDII Compliance Option and Deficiencies
    We are also proposing some changes to our deficiency provisions for
vehicles and engines meant for vehicles under 14,000 pounds. We have
included specific mention of air-fuel ratio sensors and NOX
sensors where we had long referred only to oxygen sensors. We have also
updated the referenced CARB OBDII document that can be used to satisfy
the federal OBD requirements.\48\
---------------------------------------------------------------------------

    \48\ See 13 CCR 1968.2, released August 11, 2006, Docket
ID EPA-HQ-OAR-2005-0047-0005.
---------------------------------------------------------------------------

I. How Do the Proposed Requirements Compare to California's?

    The California Air Resources Board (CARB) has its own OBD
regulations for engines used in vehicles over 14,000 pounds GVWR.\49\
(13 CCR 1971.1) In August of 2004, EPA and CARB signed a memorandum of
agreement to work together to develop a single, nationwide OBD program
for engines used in vehicles over 14,000 pounds.\50\ We believe that,
for the most part, we have been successful in doing so at least for the
early years of implementation. Nonetheless, there are differences in
some of the details contained within each regulation. These differences
are summarized here and we request comment on all of these differences.
---------------------------------------------------------------------------

    \49\ 13 CCR 1971.1, Docket ID EPA-HQ-OAR-2005-0047-
0006.
    \50\ ``Memorandum of Agreement: On-road Heavy-duty Diagnostic
Regulation Development,'' signed by Chet France, U.S. EPA, and Tom
Cackette, California ARB, August 11, 2004, Docket ID EPA-
HQ-OAR-2005-0047-0002.
---------------------------------------------------------------------------

    The first difference is that the CARB regulation contains some more
stringent thresholds beginning in the 2013 timeframe for some engines
and 2016 for all engines. Specifically, CARB's PM threshold for diesel
particulate filters (DPF) and exhaust gas sensors downstream of
aftertreatment devices, and their NOX threshold for
NOX aftertreatment devices and exhaust gas sensors
downstream of aftertreatment devices, become more stringent in 2013 for
some engines and 2016 for all. We are not proposing these more
stringent thresholds--our proposed thresholds are shown in Table II.B-
1. At this time, EPA is not in a position to propose these more
stringent OBD thresholds for the national program. The industry
believes that CARB's more stringent NOX and PM thresholds
for 2013 and 2016 are not technically feasible. EPA is reviewing these
longer term OBD thresholds, but at this time we have not made a
decision regarding the feasibility and the appropriateness of these
longer term thresholds. Because these thresholds do not take effect
until model year 2013 at the earliest, we do not believe it is
necessary to make such a determination in this rulemaking. It would be
our intention to monitor the progress made towards complying with the
2010 thresholds contained in today's proposal and potentially revisit
the appropriateness of more stringent OBD thresholds for model year
2013 and later in the future. CARB has made commitments to review their
HD OBD program every two years and they can consider making changes to
their long-term program during this biennial review process. EPA's
regulatory development process does not lend itself to making updates
every two years because the Federal rulemaking process tends to be
lengthier than CARB's. As mentioned above, we intend to monitor the
CARB long-term thresholds during the coming years, and if we determine
that more stringent thresholds are appropriate, we would consider
changing our thresholds to include the more stringent thresholds
through a notice and comment rulemaking process.
    CARB also has some slightly different certification demonstration
requirements in the 2011 and 2012 model years. They are requiring
demonstration testing of the child ratings from the 2010 model year
certified engine family for 2011 and 2012 model year certification. As
Table II.B-1 shows, we are not requiring such demonstration testing in
the 2011 and 2012 model years provided the child ratings meet the
requirements of certification carry-over. Further, CARB is requiring
that one engine rating from one to three engine families undergo full
certification demonstration testing in the 2013 model year and every
model year thereafter. In contrast, EPA is requiring that one to three
engine ratings be fully demonstrated in the 2013 model year and then
carry-over through the 2015 model year (again, provided the engine
ratings meet the requirements of certification carry-over). In 2016 and
subsequent model years, EPA would require that one to three engine
ratings be fully demonstrated on an ``as needed'' basis. In the same
vein, our evaluation protocol associated with certification
demonstration testing, as discussed in section VIII.C, requires less
testing than is required in CARB's regulation.
    Our OBD requirements for over 14,000 pounds do not contain any
provisions to monitor control strategies associated with idle emission
control strategies because EPA does not have currently any regulatory
requirements that specifically target idle emissions control
strategies.\51\ We are not proposing a provision to charge fees
associated with OBD deficiencies as CARB does. We are also not
proposing provisions for ``retroactive deficiencies'' as CARB has. Our
deficiency provisions along with our misbuild and other in-use
enforcement programs accomplish the same thing. Deficiencies are
discussed in section VIII.D.\52\
---------------------------------------------------------------------------

    \51\ Note that, by idle emission control strategies we mean
strategies that, for example, shut down the engine after 10 minutes
of constant idle. We do not mean strategies that control emissions
during engine idles that occur at stop lights or in congested
traffic.
    \52\ See also proposed Sec.  86.010-18(n).
---------------------------------------------------------------------------

    For diesel engines used in heavy-duty vehicles under 14,000 pounds,
our proposed OBD requirements are in line with those recently proposed
by CARB.\53\ Our proposed requirements are also in line--both the
technical aspects and the implementation timing aspects--with our
proposed requirements for over 14,000 pound diesel applications. We are
also proposing diesel vehicle-based OBD requirements in line with the
proposed diesel engine-based requirements. In contrast, CARB does not
have diesel thresholds in terms of ``grams per mile'' specified in
their regulation for the 8,500 to 14,000 pound range.
---------------------------------------------------------------------------

    \53\ See 13 CCR 1968.2, released August 11, 2006, Docket
ID EPA-HQ-OAR-2005-0047-0005.
---------------------------------------------------------------------------

    Specifically for gasoline engines meant for applications over
14,000 pounds, our proposal differs from CARB's in that we are not
requiring detection of catalysts that are less than 50 percent
effective at converting emissions.\54\ We are not requiring this
because we are relying on the emissions threshold of 1.75 times the
applicable standard as a means of defining a catalyst system
malfunction. We are also proposing some differences with respect to
misfire monitoring. Most notably, we are not proposing a provision
analogous

to CARB's provision that allows the Executive Officer to approve
misfire monitor disablement or alternative malfunction criteria on a
case by case basis.\55\ In general, we prefer to avoid having
regulatory provisions that are implemented on a case by case basis. For
similar reasons, we are also not proposing a provision analogous to
CARB's provision that allows the Executive Officer to revise the
orifice for evaporative leak detection if the most reliable monitoring
strategy cannot detect the required orifice.\56\
---------------------------------------------------------------------------

    \54\ See 13 CCR 1971.1(f)(6.2.1)(B) and compare to proposed
Sec.  86.010-18(h)(6)(ii).
    \55\ See 13 CCR 1971.1(f)(2.3.4)(D) and compare to proposed
Sec.  86.010-18(h)(2)(iii)(D).
    \56\ See 13 CCR 1971.1(f)(7.2.3) and compare to proposed Sec.
86.010-18(h)(7)(ii)(B) and (C).
---------------------------------------------------------------------------

III. Are the Proposed Monitoring Requirements Feasible?

    Some of the OBD monitoring strategies discussed here would be
intrusive monitors that would result in very brief emissions increases,
or spikes, for the sake of determining if certain emissions control
components/systems are working properly during the remaining 99 percent
or more of the engine's operation. While these emissions spikes are
brief, and their levels cannot be meaningfully predicted or estimated,
we are concerned about strategies that might give little concern to
emissions during such spikes in favor of an easier monitor. We request
comment on this issue--should such strategies be allowed or should such
strategies be prohibited? If a commenter has the latter opinion, then
suggestions should be provided for how the monitoring requirements
should be changed to allow for a non-intrusive monitor--i.e., one that
could run during normal operation or operation ``on the cycle''--that
may not provide the monitoring capability nor the control expected by
the requirements we are proposing.

A. Feasibility of the Monitoring Requirements for Diesel/Compression-
Ignition Engines

1. Fuel System Monitoring
a. Fuel Pressure Monitoring
    Manufacturers control fuel pressure by using a closed-loop feedback
algorithm that allows them to increase or decrease fuel pressure until
the fuel pressure sensor indicates they have achieved the desired fuel
pressure. For the common-rail OBD systems certified in the under 14,000
pound category, the manufacturers are monitoring the actual fuel system
pressure sensed by a fuel rail pressure sensor, comparing it to the
target fuel system pressure stored in a software table or calculated by
an algorithm inside the onboard computer, and indicating a malfunction
if the magnitude of the difference between these two exceeds an
acceptable level. The error limits are established by engine
dynamometer emission tests to ensure that a malfunction would be
detected before emissions exceed the applicable thresholds.
    In cases where no fuel pressure error can generate a large enough
emission increase to exceed the applicable thresholds, manufacturers
are required to set the malfunction trigger at their fuel pressure
control limits (e.g., when they reach a point where they can no longer
increase or decrease fuel pressure to achieve the desired fuel
pressure). This monitoring requirement has been demonstrated as
technically feasible given that several under 14,000 pound diesels
already meet this requirement. Further, the nature of a closed-loop
algorithm is that such a system is inherently capable of being
monitored because it simply requires analysis of the same closed-loop
feedback parameter being used by the system for control purposes.
    Another promising technology is a pressure sensing glow plug. The
glow plug is an electronic device in the cylinder of most diesel
engines used to facilitate combustion during cold engine starting
conditions. Glow plugs are being developed that incorporate a pressure
sensor capable of detecting the quality of combustion within the
cylinder.\57\ Pressure-sensing glow plugs provide feedback to the
engine-management system that controls the timing and quantity of fuel
injected into the cylinder. This feedback allows the engine electronics
to adjust the injection characteristics so the engine avoids fuel-
mixture combinations that generate high levels of NOX. In
this sense, a feedback loop is available that works like the oxygen
sensor in a gasoline engine exhaust system. By measuring the quality of
combustion, a determination can also be made about the quality of the
fuel injection event--the pressure of fuel delivered, quantity of fuel
delivered, timing of fuel delivered.
---------------------------------------------------------------------------

    \57\ ``Spotlight on Technology: Smart glowplugs may make Clean
Diesels cost-effective Pressure-sensing units could let designers
cut NOX aftertreatment,'' Tony Lewin, Automotive News,
February 6, 2006.
---------------------------------------------------------------------------

b. Fuel Injection Quantity Monitoring
    Absent combustion sensors and/or pressure sensing glow plugs
mentioned above, there is currently no feedback sensor indicating that
the proper quantity of fuel has been injected. Therefore, injection
quantity monitoring will be more difficult than pressure monitoring.
Nonetheless, a manufacturer has identified a strategy currently being
used that verifies the injection quantity under very specific engine
operating conditions and appears to be capable of determining that the
system is accurately delivering the desired fuel quantity. This
strategy entails intrusive operation of the fuel injection system
during a deceleration event where fuel injection is normally shut off
(e.g., coasting or braking from a higher vehicle speed down to a low
speed or a stop). During the deceleration, fuel injection to a single
cylinder is turned back on to deliver a very small amount of fuel.
Typically, the amount of fuel would be smaller than, or perhaps
comparable to, the amount of fuel injected during a pilot or pre-
injection. If the fuel injection system is working correctly, that
known injected fuel quantity will generate a known increase in
fluctuations (accelerations) of the crankshaft that can be measured by
the crankshaft position sensor. If too little fuel is delivered, the
measured crankshaft acceleration will be smaller than expected. If too
much fuel is delivered, the measured crankshaft acceleration will be
larger than expected. This process can even be used to ``balance'' out
each cylinder or correct for system tolerances or deterioration by
modifying the commanded injection quantity until it produces the
desired crankshaft acceleration and applying a correction or adaptive
term to that cylinder's future injections. Each cylinder can, in turn,
be cycled through this process and a separate analysis can be made for
the performance of the fuel injection system for each cylinder. Even if
this procedure would require only one cylinder be tested per revolution
(to eliminate any change in engine operation or output that would be
noticeable to the driver) and require each cylinder to be tested on
four separate revolutions, this process would only take two seconds for
a six cylinder engine decelerating through 1500 rpm.
    The crankshaft position sensor is commonly used to identify the
precise position of the piston relative to the intake and exhaust
valves to allow for very accurate fuel injection timing control and, as
such, there exists sufficient resolution and data sampling within the
onboard computer to enable such measurement of crankshaft
accelerations. Further, in addition to the current use of this strategy
in an under 14,000 pound diesel application, a nearly identical
crankshaft fluctuation technique has been used since 1997 on under
14,000 pound diesel engines

during idle conditions to determine if individual cylinders are
misfiring.
    Another technique that may be used to achieve the same monitoring
capability is some variation on the current cylinder balance tests used
by many manufacturers to improve idle quality. In such strategies,
fueling to individual cylinders is increased, decreased, or shut off to
determine if the cylinder is contributing an equal share to the output
of the engine. This strategy again relies on changes in crankshaft/
engine speed to measure the individual cylinder's contribution relative
to known good values and/or the other cylinders. Such an approach seems
viable to determine whether the fuel injection quantity is correct for
each cylinder, but it has the disadvantage of not necessarily being
able to verify whether the system is able to deliver small amounts of
fuel precisely (such as those commanded during a pilot injection).
    One other approach that has been mentioned but not investigated
thoroughly is the use of a wide-range air-fuel (A/F) sensor in the
exhaust to confirm fuel injection quantity. The A/F sensor output could
be compared to the measured air going into the engine and calculated
fuel quantity injected to see if the two agree. Differences in the
comparison may allow for the identification of incorrect fuel injection
quantity.
c. Fuel Injection Timing Monitoring
    In the same manner as described for quantity monitoring, we believe
that fuel injection timing could be verified. By monitoring the
crankshaft speed fluctuation and, most notably, the time at which such
fluctuation begins, ends, or reaches a peak, the OBD system could
compare the time to the commanded fuel injection timing point and
verify that the crankcase fluctuation occurred within an acceptable
time delay relative to the commanded fuel injection. If the system was
working improperly and actual fuel injection was delayed relative to
when it was commanded, the corresponding crankshaft speed fluctuation
would also be delayed and would result in a longer than acceptable time
period between commanded fuel injection timing and crankshaft speed
fluctuation. A more detailed discussion of this possible monitoring
method is presented in the technical support document contained in the
docket.\58\
---------------------------------------------------------------------------

    \58\ Draft Technical Support Document, HDOBD NPRM, EPA420-D-06-
006, Docket ID EPA-HQ-OAR-2005-0047-0008.
---------------------------------------------------------------------------

    Another possible monitoring method that has been mentioned but not
investigated thoroughly would be to look for an electrical feedback
signal from the injector to the computer to confirm when the injection
occurred. Such a technique would likely use an inductive signature to
identify exactly when an injector opened or closed and verify that it
was at the expected timing. We expect that further investigation would
be needed to confirm that such a monitoring technique would be
sufficient to verify fuel injection timing.
d. Fuel System Feedback Control Monitoring
    The conditions necessary for feedback control (i.e., the feedback
enable criteria) are defined as part of the control strategy in the
engine computer. The feedback enable criteria are typically based on
minimum conditions necessary for reliable and stable feedback control.
When the manufacturer is designing and calibrating the OBD system, the
manufacturer would determine, for the range of in-use operating
conditions, the time needed to satisfy these feedback enable criteria
on a properly functioning engine. In-use, the OBD system would evaluate
the time needed for these conditions to be satisfied following an
engine start, compare that to normal behavior for the system, and
indicate a malfunction when the time exceeds a specified value (i.e.,
the malfunction criterion). For example, fuel pressure feedback control
may be calibrated to begin once fuel system pressure has reached a
minimum specified value. In a properly functioning system, pressure
builds in the system during engine cranking and shortly after starting
and the pressure enable criterion are reached within a few seconds.
However, in a malfunctioning system (e.g., due to a faulty low-pressure
fuel pump), it may take a significantly longer time to reach the
feedback enable pressure. A malfunction would be indicated when the
actual time to reach feedback enable pressure exceeds the malfunction
criterion.
    Malfunctions that cause open-loop or default operation can be
readily detected as well. As discussed above, the feedback enable
criteria are clearly defined in the computer and are based on what is
necessary for reliable control. After feedback control has begun, the
OBD system can detect these criteria and indicate a malfunction when
they are no longer being satisfied. For example, one enable criterion
could be a pressure sensor reading within a certain range where the
upper pressure limit would be based on the maximum pressure that could
be generated in a properly functioning system. A malfunction would be
indicated if the pressure sensor reading exceeded the upper limit which
would cause the fuel system to go open loop.
    The feedback control system adjusts the base fuel strategy such
that actual engine operating characteristics meet driver demand. But,
the feedback control system has limits on how much adjustment can be
made based, presumably, on the ability to maintain acceptable control.
Like the feedback enable criteria, these control limits are defined in
the computer. The OBD system would track the actual adjustments made by
the control system and continuously compare them with the control
limits. A malfunction would be indicated if the limits were reached.
    2. Engine Misfire Monitoring
    Diesel engines certified to the under 14,000 pound OBD requirements
have been monitoring for misfire since the 1998 model year. The
monitoring requirements we are proposing for over 14,000 pound
applications are identical to the existing requirements for under
14,000 pound applications for those engines that do not use combustion
sensors.\59\ Therefore, technological feasibility has been demonstrated
for these applications.
---------------------------------------------------------------------------

    \59\ Technically, the EPA OBD diesel misfire monitoring
requirement for under 14,000 pound applications is to detect a lack
of combustion whereas the California OBDII diesel misfire monitoring
requirement is identical to what we are proposing for over 14,000
pounds. Since all manufacturers to date are designing to the OBDII
requirements, this statement is, for practical purposes, true.
---------------------------------------------------------------------------

    For engines that use combustion sensors, the misfire monitoring
requirements are more stringent since the requirement calls for
detection of malfunctions causing emissions to exceed the emissions
thresholds. Nonetheless, detection on these engines should be straight
forward since the combustion sensors would provide a direct measurement
of combustion. Therefore, lack of combustion (i.e., misfire) could be
measured directly. The combustion sensors are intended to measure
various characteristics of a combustion event for feedback control.
Such feedback is needed for engines that require very precise air and
fuel metering controls such as would be required for homogeneous charge
compression ignition (HCCI) engine. Accordingly, the resolution of
sensors having that capability is well beyond what would be needed to
detect a complete lack of combustion.

3. Exhaust Gas Recirculation (EGR) Monitoring
a. EGR Low Flow/High Flow Monitoring
    Typically, the EGR control system determines a desired EGR flow
rate based on the engine operating conditions such as engine speed and
engine load. The desired EGR flow rates, and the corresponding EGR
valve positions needed to achieve the desired flow rates, are
established when the manufacturer designs and calibrates the EGR
system. Once established, manufacturers store the desired EGR flow
rate/valve position in a lookup table in the onboard computer. During
operation, the onboard computer commands the EGR valve to the position
necessary to achieve the desired flow--i.e., the commanded EGR flow.
The onboard computer then calculates or directly measures both the
fresh air charge (fresh air intake) and total intake charge. The
difference between the total intake charge and fresh air intake is the
actual EGR flow. The closed-loop control system continuously adjusts
the EGR valve position until the actual EGR flow equals the desired EGR
flow.
    Such closed-loop control strategies and their associated OBD
monitoring strategies are used on many existing gasoline and diesel
vehicles under 14,000 pounds. The OBD system evaluates the difference
(i.e., error) between the look-up value--i.e., the desired flow rate--
and the final commanded value needed to achieve the desired flow rate.
Typically, as the feedback parameter or learned offset increases, there
is an attendant increase in emissions. A correlation can be made
between feedback adjustment and emissions. When the error exceeds a
specific threshold, a malfunction would be indicated. This type of
monitoring strategy could be used to detect both high and low flow
malfunctions.
    While the closed-loop control strategy described above is effective
in measuring and controlling EGR flow, some manufacturers are currently
investigating the use of a second control loop based on an air-fuel
ratio (A/F) sensor (also known as wide-range oxygen sensors or linear
oxygen sensors) to further improve EGR control and emissions. With this
second control loop, the desired air-fuel ratio is calculated based on
engine operating conditions (i.e., intake airflow, commanded EGR flow
and commanded fuel). The calculated air-fuel ratio is compared to the
air-fuel ratio from the A/F sensor and refinements can be made to the
EGR and airflow rates--i.e., the control can be ``trimmed''--to achieve
the desired rates. On systems that use the second control loop, flow
rate malfunctions could also be detected using the feedback information
from the A/F sensor and by applying a similar monitoring strategy as
discussed above for the primary EGR control loop.
    We are also proposing that two leaking EGR valve failure modes be
detected. One type is the failure of the valve to seal when in the
closed position. For example, if the valve or seating surface is
eroded, the valve could close and seat, yet still allow some flow
across the valve. A flow check is necessary to detect a malfunctioning
valve that closes properly but still leaks. EGR flow--total intake
charge minus fresh air charge--could be calculated using the monitoring
strategy described above for high and low flow malfunctions. With the
valve closed, a malfunction would be indicated when flow exceeds
unacceptable levels. Or, some cooled EGR systems will incorporate an
EGR temperature sensor that could be used to detect a leaking EGR valve
by reacting to the presence of hot exhaust gases when none should be
present. A leaking valve can also be caused by failure of the valve to
close/seat. For example, carbon deposits on the valve or seat could
prevent the valve from closing fully. The flow check described above
could detect failure of the valve to close/seat, but this approach
would require a repair technician to further diagnose whether the
problem is a sealing or seating problem. Such a failure of the valve to
close/seat could be more specifically monitored by closing the valve
and checking the zero position of the valve with a position sensor. If
the valve position is out of the acceptable range for a closed valve, a
malfunction would be indicated. This type of zero position sensor check
is commonly used to verify the closed position of valves/actuators used
in gasoline OBD systems (e.g. gasoline EGR valves, electronic throttle)
and should be feasible for diesel EGR valves.
b. EGR Slow Response Monitoring
    While the flow rate monitor discussed above would evaluate the
ability of the EGR system to achieve a commanded flow rate under
relatively steady state conditions, the EGR slow response monitor would
evaluate the ability of the EGR system to modulate (i.e., increase and
decrease) EGR flow as engine operating conditions and, consequently,
commanded EGR rates change. Specifically, as engine operating
conditions and commanded EGR flow rates change, the monitor would
evaluate the time it takes for the EGR control system to achieve the
commanded change in EGR flow. This monitor could evaluate EGR response
passively during transient engine operating conditions encountered
during in-use operation. The monitor could also evaluate EGR response
intrusively by commanding a change in EGR flow under a steady state
engine operating condition and measuring the time it takes to achieve
the new EGR flow rate. Similar passive and intrusive strategies have
been developed for variable valve control and/or timing (VVT)
monitoring on vehicles under 14,000 pounds.
c. EGR Feedback Control Monitoring
    Monitoring of EGR feedback control could be performed using
analogous strategies to those discussed in Section III.A.1 for
monitoring of fuel system feedback control.
d. EGR Cooling System Monitoring
    Some diesel engine manufacturers currently use exhaust gas
temperature sensors as an input to their EGR control systems. On such
systems--EGR temperature--which is measured downstream of the EGR
cooler--could be used to monitor the effectiveness of the EGR cooler.
For a given engine operating condition (e.g., a steady speed/load that
generates a known exhaust mass flow and exhaust temperature to the EGR
cooler), EGR temperature will increase as the performance of the EGR
cooling system decreases. During the OBD calibration process,
manufacturers could develop a correlation between increased EGR
temperatures and cooling system performance (i.e., increased
emissions). The EGR cooling system monitor would use such a correlation
and indicate a malfunction when the EGR temperature increases to the
level that would cause emissions to exceed the emissions thresholds.
    While we anticipate that most, if not all, manufacturers will use
EGR temperature sensors to meet future emissions standards, EGR cooling
system monitoring may be feasible without such a temperature sensor.
The monitor could be done using the intake manifold temperature (IMT)
sensor by looking at the change in IMT (i.e., ``delta'' IMT) with EGR
turned on and EGR turned off (IMT would be higher with EGR turned on).
If there is significant cooling capacity with a normally functioning
EGR cooling system, there would likely be a significant difference in
IMT with EGR turned on versus turned off. Delta IMT could be correlated
to decreased EGR cooling system performance and increased emissions.

4. Turbo Boost Control System Monitoring
a. Turbo Underboost/Overboost Monitoring
    To monitor boost control systems, manufacturers are expected to
look at the difference between the actual pressure sensor reading (or
calculation thereof) and the desired/target boost pressure. If the
error between the two is too large or persists for too long, a
malfunction would be indicated. Manufacturers would need to calibrate
the size of error and/or error duration to ensure robust malfunction
detection occurs before the emissions thresholds are exceeded. Given
that the purpose of a closed-loop control system with a feedback sensor
is to measure continuously the difference between actual and desired
boost pressure, the control system is already monitoring that
difference and attempting to minimize it. As such, a monitoring
requirement to indicate a malfunction when the difference gets large
enough such that it can no longer achieve the desired boost is
essentially an extension of the existing control strategy.
    To monitor for malfunction or deterioration of the boost pressure
sensors, manufacturers could validate sensor readings against other
sensors present on the vehicle or against ambient conditions. For
example, at initial key-on before the engine is running, the boost
pressure sensor should read ambient pressure. If the vehicle is
equipped with a barometric pressure sensor, the two sensors could be
compared and a malfunction indicated when the two readings differ
beyond the specific tolerances. A more crude rationality check of the
boost pressure sensor could be accomplished by verifying that the
pressure reading is within reasonable atmospheric limits for the
conditions the vehicle will be subjected to.
b. VGT Slow Response Monitoring
    The VGT slow response monitor would evaluate the ability of the VGT
system to modulate (i.e., increase and decrease) boost pressure as
engine operating conditions and, consequently, commanded boost pressure
changes. Specifically, as engine operating conditions and commanded
boost pressures change, the monitor would evaluate the time it takes
for the VGT control system to achieve the commanded change in boost
pressure. This monitor could evaluate VGT response passively during
transient engine operating conditions encountered during in-use
operation. The monitor could also evaluate VGT response intrusively by
commanding a change in boost pressure under a steady state engine
operating condition and measuring the time it takes to achieve the new
boost pressure.
    Rationality monitoring of VGT position sensors could be
accomplished by comparing the measured sensor value to expected values
for the given engine speed and load conditions. For example, at high
engine speeds and loads, the position sensor should indicate that the
VGT position is opened more than would be expected at low engine speeds
and loads. Such rationality checks would need to be two-sided (i.e.,
position sensors should be checked for appropriate readings at both
high and low engine speed/load operating conditions.
c. Turbo Boost Feedback Control Monitoring
    Monitoring of boost pressure feedback control could be performed
using analogous strategies to those discussed for fuel system feedback
control monitoring in Section III.A.1.
d. Charge Air Undercooling Monitoring
    We expect that most engines will make use of a temperature sensor
downstream of the charge air cooler to protect against overcooling
conditions that could cause excessive condensation, and to prevent
undercooling that could result in loss of performance. A comparison of
the actual charge air temperature to the expected, or design,
temperature would indicate any errors that might be occurring.
Manufacturers could correlate that error to an emissions impact and,
when the error reached a level such that emissions would exceed the
emissions thresholds, a malfunction would be indicated.
5. Non-Methane Hydrocarbon (NMHC) Converting Catalyst Monitoring
a. NMHC Converting Catalyst Conversion Efficiency Monitoring
    Monitoring of the NMHC converting catalyst, or diesel oxidation
catalyst (DOC), could be performed similar to three-way catalyst
monitoring on gasoline engines. Three-way catalyst monitoring uses the
concept that catalyst's oxygen storage capacity correlates well with
its hydrocarbon conversion efficiency. Oxygen sensors located upstream
and downstream of the catalyst can be used to determine when its oxygen
storage capacity--and, hence, its conversion efficiency--has
deteriorated below a predetermined level.
    Determining the oxygen storage capacity would require lean air-fuel
(A/F) operation followed by rich A/F operation or vice-versa during the
catalyst monitoring event. Since a diesel engine normally operates lean
of stoichiometry, lean A/F operation would be normal operation.
However, rich A/F operation would have to be commanded intrusively when
the catalyst monitor is active. The rich A/F operation could be
achieved by injecting some fuel late enough in the four stroke process
(i.e., late injection) that the raw fuel would not combust in-cylinder.
Rich A/F operation could also be achieved using an in-exhaust fuel
injector upstream of the catalyst. During normal lean operation, the
catalyst would become saturated with stored oxygen. As a result, both
the front and rear oxygen sensors should be reading lean. When rich A/F
operation initiates, the front oxygen sensor would switch immediately
to a ``rich'' indication. For a short time, the rear oxygen sensor
should continue to read ``lean'' until such time as the stored oxygen
in the catalyst is consumed by the rich fuel mixture in the exhaust and
the rear oxygen sensor would read ``rich.'' As the catalyst
deteriorates, the delay time between the front and rear oxygen sensors
switching from their normal lean state to a rich state would become
progressively smaller because the deteriorated catalyst would have less
oxygen storage capacity. Thus, by comparing the time difference between
the responses of the front and rear oxygen sensors to the lean-to-rich
or rich-to-lean A/F changes, the performance of the catalyst could be
estimated. Although this discussion suggests the use of conventional
oxygen sensors, these sensors could be substituted with A/F sensors
which would also provide for additional engine control benefits such as
EGR trimming and fuel trimming.
    If a malfunction of the catalyst cannot cause emissions to exceed
the emissions thresholds, then only a functional monitor would be
required. A functional monitor could be done using temperature sensors.
A functioning oxidation catalyst would be expected to provide some
level of exotherm when it oxidizes HC and CO. The temperature of the
catalyst could be measured by placing one or more temperature sensors
at or near the catalyst. However, depending on the nominal conversion
efficiency of the catalyst and the duty cycle of the vehicle, the
exotherm may be difficult to discern from the inlet exhaust
temperatures. To add robustness to the monitor, the functional monitor
would need to be conducted during predetermined

operating conditions where the amount of HC and CO entering the
catalyst could be known. This may require an intrusive monitor that
actively forces the fueling strategy richer (e.g., through late or post
injection) than normal for a short period of time. If the measured
exotherm does not exceed a predetermined amount that only a properly-
working catalyst could achieve, a malfunction would be indicated. As
noted, such an approach would require a brief period of commanded rich
operation that would result in a very brief HC and perhaps a PM
emissions spike.
b. Other Aftertreatment Assistance Function Monitoring
    A functional monitor should be sufficient for monitoring the
oxidation catalyst's ability to fulfill aftertreatment assistance
functions such as generating an exotherm for DPF regeneration or
providing a proper feedgas for SCR or NOX adsorbers. We
would expect that manufacturers would use the exotherm approach
mentioned above either to measure directly for the proper exotherm or
to correlate indirectly for the proper feedgas. For catalysts upstream
of a DPF, we expect that this monitoring would be conducted during an
active or forced regeneration event.\60\ For catalysts downstream of
the DPF, we expect that manufacturers would have to add fuel
intrusively (either in-exhaust or through in-cylinder post-injection)
to create a sufficient exotherm to distinguish malfunctioning from
properly operating catalysts.
---------------------------------------------------------------------------

    \60\ An active or forced regeneration would be those
regeneration events that are initiated via a driver selectable
switch or activator and/or those initiated by computer software.
---------------------------------------------------------------------------

6. Selective Catalytic Reduction (SCR) and NOX Conversion
Catalyst Monitoring
a. SCR and NOX Catalyst Conversion Efficiency Monitoring
    We would expect manufacturers to use NOX sensors to
monitor a lean NOX catalyst. NOX sensors placed
upstream and downstream of the lean NOX catalyst could be
used to determine directly the NOX conversion efficiency.
Manufacturers could potentially use a single NOX sensor
placed downstream of the catalyst to measure catalyst-out
NOX emissions. This would have to be done within a tightly
controlled engine operation window where engine-out NOX
emissions (i.e., NOX emissions at the lean NOX
catalyst inlet) performance is relatively stable and could be estimated
reliably. Within this engine operation window, catalyst-out
measurements could be compared to the expected engine-out
NOX emissions and a catalyst conversion efficiency could be
calculated. Should the calculated conversion efficiency be insufficient
to maintain emissions below the emissions thresholds, a malfunctioning
or deteriorated lean NOX catalyst would be indicated. If
both an upstream and downstream NOX sensor are used for
monitoring, the upstream sensor could be used to improve the overall
effectiveness of the catalyst by precisely controlling the air-fuel
ratio in the exhaust to the levels where the catalyst is most
effective.
    For monitoring the SCR catalyst, care must be taken to account for
the cross sensitivity of NOX sensors to ammonia
(NH3). Current NOX sensor technology tends to
have such a cross-sensitivity to ammonia in that as much as 65 percent
of ammonia can be read as NOX.\61\ However, urea SCR
feedback control studies have shown that the NH3
interference signal is discernable from the NOX signal and
can, in effect, allow the design of a better feedback control loop than
a NOX sensor that doesn't have any NH3 cross-
sensitivity. In one study, a signal conditioning method was developed
that resulted in a linear output for both NH3 and
NOX from the NOX sensor downstream of the
catalyst.\62\ Monitoring of the catalyst can be done by using the same
NOX sensors that are used for SCR control. When the SCR
catalyst is functioning properly, the upstream sensor should read
``high'' for high NOX levels while the downstream sensor
should read ``low'' for low NOX and low ammonia levels. With
a deteriorated SCR catalyst, the downstream sensor should read similar
or higher values as the upstream sensor (i.e., high NOX and
high ammonia levels) since the NOX reduction capability of
the catalyst has diminished. Therefore, a malfunctioning SCR catalyst
could be detected when the downstream sensor output is near to or
greater than the upstream sensor output. A similar monitoring approach
could be used if a manufacturer models upstream NOX
emissions instead of using an upstream NOX sensor. In this
case, the comparison would be made between the modeled upstream
NOX value and the downstream sensor value.
---------------------------------------------------------------------------

    \61\ Schaer, C.M., Onder, C.H., Geering, H.P., and Elsener, M.,
``Control of a Urea SCR Catalytic Converter System for a Mobile
Heavy-Duty Diesel Engine,'' SAE Paper 2003-01-0776 which may be
obtained from Society of Automotive Engineers International, 400
Commonwealth Dr., Warrendale, PA, 15096-0001.
    \62\ Ibid.
---------------------------------------------------------------------------

    Manufacturers have expressed concern over both the sensitivity and
the durability of NOX sensors. They are concerned that
NOX sensors will not have the necessary sensitivity to
detect NOX at the low levels that will exist downstream of
the NOX catalyst. They are also concerned that
NOX sensors will not be durable enough to last the full
useful life of big diesel trucks. We have researched NOX
sensors--the current state of development and future expectations--and
summarized our findings in the technical support document in the docket
for this rule.\63\ Some of our findings are summarized here.
---------------------------------------------------------------------------

    \63\ Draft Technical Support Document, HDOBD NPRM, EPA420-D-06-
006, Docket ID EPA-HQ-OAR-2005-0047-0008.
---------------------------------------------------------------------------

    Regarding NOX sensor sensitivity, we expect that 2010
and later model year engines will have average tailpipe NOX
emissions in the 0 to 50 ppm range. Current NOX sensors have
an accuracy of 10 ppm in the 0 to 100 ppm range. This means
that current NOX sensors should be able to detect
NOX emissions that exceed the standard by two to three times
the 2010 limit.\64\ This should allow for compliance with our proposed
threshold which is effectively 2.5 times the 2010 limit. Further, we
expect that NOX sensors in the 0 to 100 ppm range with
5 ppm accuracy will be available by the middle of 2006.
Regarding durability, improvements are being made and a test program is
currently underway with the intent of aging several NOX
sensors placed at various exhaust system locations out to 6,000 hours
(roughly equivalent to 360,000 miles). Results after 2,000 hours of
aging are promising and results after 4,000 hours of aging are
currently being analyzed.\65\
---------------------------------------------------------------------------

    \64\ Ibid.
    \65\ Ibid.
---------------------------------------------------------------------------

b. SCR and NOX Catalyst Active/Intrusive Reductant Injection
System Monitoring
    If an active catalyst system is used--i.e., one that relies on
injection of a reductant upstream of the catalyst to assist in
emissions conversion--manufacturers would be required to monitor the
mechanism for adding the fuel reductant. In the active catalyst system,
a temperature sensor is expected to be placed near or at the catalyst
to determine when the catalyst temperature is high enough to convert
emissions. Because NOX catalyst systems, especially lean
NOX catalyst systems, tend to have a narrow temperature
range where they are most effective, adding reductant when the catalyst
temperature is not sufficiently high would waste reductant. If fuel is

used as the reductant, this would adversely affect fuel economy without
a corresponding reduction in emissions levels. Therefore, a temperature
sensor is expected to be placed in the exhaust near or at the catalyst
to help determine when reductant injection should occur. This same
sensor could be used to determine if an exotherm resulted following
reductant injection. The lack of an exotherm would indicate a
malfunction of the reductant delivery system.
    Alternatively, any NOX sensors used to monitor
conversion efficiency could be used to determine if reductant injection
has occurred. NOX sensors are also oxygen sensors so they
could be used to determine the air-fuel ratio in the exhaust stream
which would allow for verification of reductant injection into the
exhaust. Further, with a properly functioning injector, the downstream
NOX sensor should see a change from high NOX
levels to low NOX levels. In contrast, a lack of reductant
injection would result in continuously high NOX levels at
the downstream NOX sensor. Therefore, a malfunctioning
injector could be indicated when the downstream NOX sensor
continues to measure high NOX after an injection event has
been commanded.
    Reductant level monitoring could also be conducted by using the
existing NOX sensors that are used for control purposes.
Specifically, the downstream NOX sensor can be used to
determine if the reductant tank no longer has sufficient reductant
available. Similar to the fuel reductant injection functionality
monitor described above, when the reductant tank has a sufficient
reductant quantity and the injection system is working properly, the
downstream NOX sensor should see a change from high
NOX levels to low NOX levels. If the
NOX levels remain constant both before and after reductant
injection, then the reductant was not properly delivered and either the
injection system is malfunctioning or there is no longer sufficient
reductant available in the reductant tank. Alternatively, reductant
level monitoring could be conducted by using a dedicated ``float'' type
level sensor similar to the ones used in fuel tanks. Some manufacturers
may prefer using a dedicated reductant level sensor in the reductant
tank to inform the vehicle operator of current reductant levels via a
gauge on the instrument panel. If such a sensor is used by the
manufacturer for operator convenience, it could also be used to monitor
the reductant level in the tank.
    Monitoring the reductant itself--whether it be the wrong reductant
or a poor quality reductant--could also be conducted using the
NOX sensors used for control purposes. If an improper
reductant is injected, the NOX catalyst system would not
function properly. Therefore, NOX emissions downstream from
the catalyst would remain high both before and after injection. The
downstream NOX sensor would see the high NOX
levels after injection and a malfunction would be indicated. If the
reductant tank level sensor indicated sufficient levels for injection
and decreasing levels following injections (which would mean the
injection system was working), then the probable cause of the
malfunction would be the reductant itself. For urea SCR systems,
another possible means of monitoring the reductant itself would be to
use a urea quality sensor in the urea tank. First generation sensors
show promise at verifying that urea is indeed in the tank, rather than
water or some other fluid, and that the urea concentration is within
the needed range (i.e., not diluted with water or some other fluid).
The sensor could also be used in place of a urea level sensor. By 2010,
we would expect subsequent generation sensors to provide even better
capability.\66\
---------------------------------------------------------------------------

    \66\ Crawford, John M., Mitsui Mining & Smelting Co., Ltd.,
presentation to EPA, October 2006, Docket ID EPA-HQ-OAR-
2005-0047-0007.
---------------------------------------------------------------------------

c. SCR and NOX Catalyst Feedback Control Monitoring
    Monitoring of feedback control could be performed using analogous
strategies to those discussed for fuel system feedback control
monitoring in Section III.A.1.
7. NOX Adsorber Monitoring
a. NOX Adsorber Capability Monitoring
    We expect that either NOX sensors or A/F sensors along
with a temperature sensor will be used to provide the feedback
necessary to control the NOX adsorber system. These same
sensors could also be used to monitor the NOX adsorber
system's capability. The use of NOX sensors placed upstream
and downstream of the adsorber system would allow the system's
NOX reduction performance to be continuously monitored. For
example, the upstream NOX sensor on a properly functioning
adsorber system operating with lean fuel mixtures, will read high
NOX levels while the downstream NOX sensor should
read low NOX levels. With a deteriorated NOX
adsorber system, the upstream NOX levels will continue to be
high while the downstream NOX levels will also be high.
Therefore, a malfunction of the system can be detected by comparing the
NOX levels measured by the downstream NOX sensor
versus the upstream sensor.
    The possibility exists that an upstream NOX sensor will
not be used for NOX adsorber control. Manufacturers may
choose to model engine-out NOX levels--based on engine
operating parameters such as engine speed, fuel injection quantity and
timing, EGR flow rate--thereby eliminating the need for the upstream
NOX sensor. In this case, we believe that monitoring of the
system could be conducted using A/F sensors in place of NOX
sensors.\67\ During lean engine operation with a properly operating
NOX adsorber system, both the upstream and downstream A/F
sensors would indicate lean mixtures. When the exhaust gas is
intrusively commanded rich to regenerate the NOX adsorber,
the upstream A/F sensor would quickly indicate a rich mixture while the
downstream sensor should continue to see a lean mixture due to the
chemical reaction of the reducing agents with NOX and oxygen
stored on the adsorber. Once all of the stored NOX and
oxygen has been released, the reducing agents in the exhaust would
cause the downstream A/F sensor to indicate a rich reading. The more
NOX that is stored in the adsorber, the longer the delay
between the rich indications from the upstream and downstream sensors.
Thus, the time differential between the rich indications from the
upstream and downstream A/F sensors is a gauge of the NOX
storage capacity of the adsorber. This delay could be correlated to an
emissions increase and the monitor could be calibrated to indicate a
malfunction upon detecting an unacceptably short delay. In fact, Honda
currently uses a similar approach to monitor the NOX
adsorber on a 2003 model year gasoline vehicle which demonstrates the
viability of the approach in a shorter lived application. We have
studied A/F sensors and their durability with respect to longer lived
diesel applications and our results are summarized in a report placed
in the docket to this rule.\68\
---------------------------------------------------------------------------

    \67\ Ingram, G.A. and Surnilla, G., ``On-Line Estimation of
Sulfation Levels in a Lean NOX Trap,'' SAE Paper 2002-01-
0731 may be obtained from Society of Automotive Engineers
International, 400 Commonwealth Dr., Warrendale, PA 15096-0001.
    \68\ Draft Technical Support Document, HDOBD NPRM, EPA420-D-06-
006, Docket ID EPA-HQ-OAR-2005-0047-0008.

---------------------------------------------------------------------------

b. NOX Adsorber Active/Intrusive Reductant Injection System
Monitoring
    The injection system used to achieve NOX regeneration of
the NOX adsorber could also be monitored with A/F sensors.
When the control system injects extra fuel to achieve a rich mixture,
the upstream A/F sensor would respond to the change in fueling and
could measure directly whether or not the proper amount of fuel had
been injected. If manufacturers employ a NOX adsorber system
design that uses only a single A/F sensor downstream of the adsorber,
that downstream sensor could be used to monitor the performance of the
injection system. As discussed above, the downstream sensor would
switch from a lean reading to a rich reading when the stored
NOX has been completely released and reduced. If the sensor
switches too quickly after rich fueling is initiated, then either too
much fuel has been injected or the adsorber itself has poor storage
capability. Conversely, if the sensor takes too long to switch after
rich fueling is initiated, it may be an indication that the adsorber
has very good storage capability. However, excessive switch times
(i.e., times that exceed the maximum storage capability of the
adsorber) could be indicative of an injection system malfunction (i.e.,
insufficient fuel has been injected) or a sensor malfunction (i.e., the
sensor has a slow response).
c. NOX Adsorber Feedback Control Monitoring
    Monitoring of feedback control could be performed using analogous
strategies to those discussed for fuel system feedback control
monitoring in Section III.A.1.
8. Diesel Particulate Filter (DPF) Monitoring
a. PM Filtering Performance Monitoring
    The PM filtering performance monitor is perhaps the monitor for
which we have the most concern with respect to feasibility. Part of
this concern stems from the difficulty in detecting the very low PM
emissions levels required for 2007/2010 engines (i.e., 0.01 g/bhp-hr).
While we have made changes to our test procedures that will allow for
more accurate measurement of PM in the test cell, it is still very
difficult to do. With today's proposal, we are expecting manufacturers
to detect failures in the filtering performance of only a few times the
actual standards. Success at doing so presents a very difficult
challenge to manufacturers. Our concerns, in part, have led us to
propose a different 2013 and later emissions threshold for this monitor
than that proposed by ARB. This was discussed in more detail in section
I.D.2.
    We anticipate that manufacturers can meet the proposed PM filtering
monitor requirements without adding hardware other than that used for
control purposes. We believe that the same pressure and temperature
sensors that are used to control DPF regeneration will be used for OBD
monitoring. For control purposes, manufacturers generally use a
differential or delta pressure sensor placed across the DPF and at
least one temperature sensor located near the DPF. The differential
pressure sensor is expected to be used on DPF systems to prevent damage
that could be caused by delayed or incomplete regeneration. Such
conditions could lead to excessive temperatures and melting of the DPF
substrate. When the differential pressure exceeds a predetermined
level, a regeneration event would be initiated to burn the trapped PM.
    However, engine manufacturers have told us that differential
pressure alone does not provide a robust indication of trapped PM in
the DPF. For example, most if not all DPFs in the 2010 timeframe will
be catalyzed DPFs that are designed to regenerate passively during most
operation. Sometimes, conditions will not permit the passive
regeneration and an active regeneration would have to be initiated.
Relying solely on the differential pressure sensor to determine when an
active regeneration event was necessary would not be sufficient. A low
differential pressure could mean a low PM load and could also mean a
leaking DPF substrate. A high differential pressure could mean a high
PM load and could also mean a melted substrate. In the latter case, the
system may continually attempt to regenerate the DPF despite a low PM
load which would both waste fuel and increase HC emissions.
    As a result, manufacturers will probably use some sort of soot-
loading model to predict the PM load on the DPF as part of their
regeneration strategy. Without a robust prediction, a regeneration
event could be initiated too early (i.e., when too little PM was
present which would be a waste of fuel and would increase HC emissions)
or too late (i.e., when too much PM has been allowed to build and the
regeneration event could cause a meltdown of the substrate). The model
would estimate the PM load by tracking the difference between the
modeled engine-out PM (i.e., the emissions that are being loaded on the
DPF) and regenerated PM (i.e., the PM that is being burned off the DPF
due to passive and/or active regenerations).
    Given this, we believe that a comprehensive and accurate soot-
loading model is also necessary for successful monitoring of DPF
filtering performance. The model would predict the PM load on the DPF
based on fuel consumption and engine operating conditions and would
predict passively regenerated PM based on temperatures. This predicted
PM load would be compared to the measured PM load taken from the
differential pressure sensors. Differences would correspond to either a
leaking substrate (i.e., predicted load greater than measured load) or
melting of the substrate faceplate (i.e., measured load greater than
predicted load).
    Nonetheless, much development remains to be done and success is not
guaranteed. Manufacturers have noted that a melted substrate through
which a large channel has opened could have differential pressure
characteristics identical to a good substrate despite allowing most of
the engine-out PM to flow directly through. We agree that this is a
difficult failure mode and have proposed language that would allow
certification of DPF monitors that are unable to detect it. Possibly, a
temperature sensor in the DPF could detect the extreme temperatures
capable of causing such a severe substrate melting. Upon detecting such
a temperature, a regeneration event could be initiated to burn off any
trapped PM. Following that event, the soot model would expect a certain
increase in differential pressure based on modeled engine-out PM and
passive regeneration characteristics. Presumably, the measured
differential pressure profile would not match the predicted profile
because most PM would be flowing straight through the melted channel.
This same approach, or perhaps a simple temperature sensor, should
quite easily be able to detect a missing substrate.
    Lastly, manufacturers have noted their concern that small
differences in substrate crack size or location may generate large
differences in tailpipe emission levels. They have also noted their
lack of confidence that they will be able to reliably detect all leaks
that would result in emissions exceeding the proposed thresholds.
Accordingly, the manufacturers have suggested pursuing an alternate
malfunction criterion independent of emission level. They have
suggested criteria such as a percent of exhaust flow leakage or a
specific leak or hole size that must be detected. We believe that
pursuit of such alternate thresholds would not be appropriate at this
time. Manufacturers have not yet completed work on initial widespread

implementation of DPFs for the 2007 model year. We expect that during
the year or two following that implementation, substantial refinement
and optimization will occur based on field experiences and that
correlation of sensor readings to emissions levels will be possible for
at least some DPF failure modes by the 2010 model year.
b. DPF Regeneration Monitoring
    Pressure sensing, in combination with the soot model, could also be
used to determine if regeneration is functioning correctly. After a
regeneration event, the differential pressure should drop significantly
since the trapped PM has been removed. If it does not drop to within
the soot model's predicted range after the regeneration event, either
the regeneration did not function correctly or the filter could have
excessive ash loading. Ash loading is a normal byproduct of engine
operation (the ash loading is largely a function of oil consumption by
the engine and the ash content of the engine oil). The ash builds up in
the DPF and does not burnout as does the PM but rather must be removed
or blown out of the DPF. Manufacturers are working with us to determine
the necessary maintenance intervals at which this ash removal will
occur. The soot model would have to account for ash buildup in the DPF
with miles or hours of operation. Future engine oils will have lower
ash content and have tighter quality control such that more accurate
predictions of ash loading will be possible. By including ash loading
in the soot model, we believe that its effects could be accounted for
in the predicted differential pressure following a regeneration event.
    As stated, manufacturers are projected to make use of temperature
sensors for regeneration control. These same sensors could also be used
to monitor active regeneration of the filter. If excess temperatures
are seen by the temperature sensor during active regeneration, the
regeneration process can be stopped or slowed down to protect the
filter. If an active regeneration event is initiated and there a
temperature rise commensurate with the amount of trapped PM is not
detected, the regeneration system is not working and a malfunction
would be indicated.
c. DPF NMHC Conversion Efficiency Monitoring
    Given the stringency of the 2010 standards, we believe that
manufactures may rely somewhat on the DPF to convert some of the HC
emissions. The proposed requirement requires monitoring this function
only if the system serves this function. We believe that, provided the
filtering performance and regeneration system monitors have not
detected any malfunctions, the NMHC conversion is probably working
fine. Given the level of the threshold, and the expectation that the
DPF will serve to control NMHC only marginally, we do not anticipate
this monitor needing emissions correlation work. Instead, we expect
that, with the DPF temperature sensor, it should be possible to infer
adequate NMHC conversion by verifying an exotherm. Nonetheless, if a
manufacturer relies so heavily on the DPF for NMHC conversion that its
ability to convert could be compromised to the point of emissions
exceeding the threshold, a more robust monitor may be required by
correlating exotherm levels to NMHC impacts.
d. DPF Regeneration Feedback Control Monitoring
    Monitoring of DPF regeneration feedback control could be performed
using analogous strategies to those discussed for fuel system feedback
control monitoring in Section III.A.1.
9. Exhaust Gas Sensor Monitoring
    The under 14,000 pound OBD regulations have required oxygen sensor
monitoring since the 1996 model year. Vehicles have been certified
during that time meeting the requirements. The technological
feasibility of monitoring oxygen sensors has been demonstrated.
Additionally, A/F sensor monitoring has been required, manufacturers
have complied, and the feasibility has been similarly demonstrated.
    NOX sensors are a recent technology and, as such, they
are still being developed and improved. However, we would expect that
manufacturers would design their upstream NOX sensor
monitors to be similar the A/F sensor monitors used in under 14,000
pound applications. Monitoring of downstream sensors may require
modifications to existing A/F sensor strategies and/or new strategies.
Since NOX sensors are projected to be used only for control
and monitoring of aftertreatment systems that reduce NOX
emissions (e.g., SCR systems), the OBD system would have to distinguish
between deterioration of the aftertreatment system and the
NOX sensor itself. As the aftertreatment deteriorates,
NOX emissions downstream of the aftertreatment device will
increase and, assuming there is no such deterioration in the
NOX sensor, the NOX sensor will read these
increasing NOX levels. As discussed in sections III.A.6 and
III.A.7, the increased NOX levels can be the basis for
monitoring the performance of the aftertreatment system. However, if
the NOX sensor does deteriorate with the aftertreatment
device (i.e., its response rate slows with mileage/operating hours),
the sensor may not properly read the increasing NOX levels
from the deteriorating aftertreatment system, and the aftertreatment
monitor might conclude that the aftertreatment system is functioning
properly. Similarly, the performance or level of deterioration of the
NOX aftertreatment device could affect the results of the
NOX sensor monitor. Therefore to achieve robust monitoring
of aftertreatment and sensors, the OBD system has to distinguish
between deterioration of the aftertreatment system and deterioration of
the NOX sensor. To properly monitor the NOX
sensor, the sensor monitor has to run under conditions where the
aftertreatment performance can be quantified and compensated for or
eliminated in the monitoring results.
    For example, the effects of the SCR performance could be eliminated
by monitoring the NOX sensor under a steady-state operating
condition during which engine-out NOX emissions were stable.
Under a relatively steady-state condition, reductant injection could be
``frozen'' (i.e., the reductant injection quantity could be held
constant) which would also freeze the conversion efficiency of the SCR
system. With SCR performance held constant, engine-out NOX
emissions could be intrusively increased by a known amount (e.g., by
reducing EGR flow or changing fuel injection timing and allowing the
engine-out NOX model to determine the increase in
emissions). The resulting increase in emissions would pass through the
SCR catalyst unconverted, and the sensor response to the known increase
in NOX concentrations could be measured and evaluated. This
strategy could be used to detect both response malfunctions (i.e., the
sensor reads the correct NOX concentration levels but the
sensor reading does not change fast enough to keep up with changing
exhaust NOX concentrations) and rationality malfunctions
(i.e., the sensor reads the wrong NOX level). Rationality
malfunctions could be detected by making sure the sensor reading
changes by the same amount as the intrusive change in emissions.
Lastly, the sensor response to decreasing NOX concentrations
could also be evaluated by measuring the response when the intrusive
strategy is turned off and engine-out NOX emissions are
returned to normal levels. By correlating sensor response rates and the
resulting

emissions impacts, the malfunction criteria could then be determined.

B. Feasibility of the Monitoring Requirements for Gasoline/Spark-
Ignition Engines

1. Fuel System Monitoring
    For gasoline vehicles since the 1996 model year and gasoline
engines since the 2005 model year, the under 14,000 pound OBD
requirements have required fuel system monitoring identical to that
being proposed. Over 100 million cars and light trucks have been built
and sold in the U.S. to these fuel system monitoring requirements
including some heavy-duty vehicles that use the exact same gasoline
engines that are used in some over 14,000 pound applications. This
clearly demonstrates the technological feasibility of the proposed
requirements.
2. Engine Misfire Monitoring
    For gasoline vehicles since the 1996 model year and gasoline
engines since the 2005 model year, the under 14,000 pound OBD
requirements have required misfire monitoring identical to that being
proposed. One of the most reliable methods for detecting misfire is the
use of a crankshaft position sensor--which measures the fluctuations in
engine angular velocity to determine the presence of misfire--along
with a camshaft position sensor--which can be used to identify the
misfiring cylinder. This method has been shown to be technologically
feasible and should work equally well on over 14,000 pound
applications.
3. Exhaust Gas Recirculation (EGR) Monitoring
    For vehicles since the 1996 model year and engines since the 2005
model year, the under 14,000 pound OBD requirements have required EGR
system monitoring identical to that being proposed. The general
approach has been to detect EGR flow rate malfunctions by looking at
the change in fuel trim or manifold pressure under conditions when the
EGR system is active. This demonstrates the technological feasibility
of the proposed requirements.
4. Cold Start Emission Reduction Strategy Monitoring
    We expect this monitoring to be done mainly via computer software.
For example, if spark retard is used during cold starts, the commanded
amount of spark retard would have to be monitored if the amount of
spark retard can be restricted by external factors such as idle quality
or driveability. This can be done with software algorithms that compare
the actual overall commanded final ignition timing with the threshold
timing that would result in emissions that exceed the emissions
thresholds. Cold start strategies that always command a predetermined
amount of ignition retard independent of all other factors and do not
allow idle quality or other factors to override the desired ignition
retard would not require monitoring of the commanded timing. Other
methods that could be used to ensure that the actual timing has been
reached include verifying other factors such as corresponding increases
in mass air flow and idle speed indicative of retarded spark
combustion. Both mass air flow and idle speed are used currently by the
engine control system and the OBD system and, therefore, only minor
software modifications should be required to analyze these signals
while the cold start strategy is invoked.
5. Secondary Air System Monitoring
    A/F sensors would most likely be required to monitor effectively
the secondary air system when it is normally active. These sensors are
currently installed on many new cars and their implementation is
projected to increase in the future as more stringent emission
standards are phased in. A/F sensors are useful in determining air-fuel
ratio over a broader range than conventional oxygen sensors and are
especially valuable in engines that require very precise fuel control.
They would be useful for secondary air system monitoring because of
their ability to determine air-fuel ratio with high accuracy. This
would enable a correlation between secondary airflow rates and
emissions.
6. Catalytic Converter Monitoring
    A common method used for estimating catalyst efficiency is to
measure the catalyst's oxygen storage capacity. This monitoring method
has been used by all light-duty gasoline vehicles since the 1996 model
year and most gasoline engines since the 2005 model year as a result of
our under 14,000 OBD requirements. Generally, as the catalyst's oxygen
storage capacity decreases, the conversion efficiencies of HC and
NOX also decrease. With this strategy, a catalyst
malfunction would be detected when its oxygen storage capacity has
deteriorated to a predetermined level. Manufacturers determine this by
using the information from an upstream oxygen sensor and a downstream
or mid-bed oxygen sensor (this second sensor is also used for trimming
the front sensor to maintain more precise fuel control). By comparing
the level of oxygen measured by the second sensor with that measured by
the upstream sensor, manufacturers can determine the catalyst's oxygen
storage capacity and estimate its conversion efficiency. With a
properly functioning catalyst, the second oxygen sensor signal will be
fairly steady since the fluctuating oxygen concentration (due to fuel
system cycling around stoichiometry) at the inlet of the catalyst is
damped by the storage and release of oxygen in the catalyst. When a
catalyst is deteriorated it is no longer capable of storing and
releasing oxygen. This causes the frequency and peak-to-peak voltage of
the second oxygen sensor to simulate the signal from the upstream
oxygen sensor at which time a malfunction would be indicated.
7. Evaporative System Monitoring
    Our OBD requirements have required monitoring for evaporative
system leaks for many years. The EPA OBD requirement has been the
equivalent of a 0.040 inch hole, while the ARB requirement has gone as
low as a 0.020 inch hole. These requirements have been met on
applications such as incomplete trucks and engine dynamometer certified
configurations equipped with similar and, in many cases, identical
configurations as are used in over 14,000 pound applications.
Manufacturers have successfully met these requirements by using engine
vacuum to create a vacuum in both the fuel tank and evaporative system
and then monitoring the system's ability to maintain that vacuum. The
ramp down in vacuum (or ramp up in pressure) can then be correlated to
leak size. In general, these systems require the addition of an
evaporative system pressure sensor and a canister vent valve capable of
closing the vent line.
    Manufacturers of over 14,000 pound applications have expressed
concerns with their ability to detect evaporative system leaks on these
larger vehicles. One such concern relates to the relatively larger fuel
tank sizes on the larger applications. These tanks can be on the order
of 50 to 80 gallons, which makes the impact of a small hole, on a
percentage basis, less severe and less easily detected. Another concern
is the relatively large number of fuel tank and evaporative system
configurations on the larger applications. Confounding both of these
concerns is that the engine manufacturers quite often have no idea what
tanks and configurations will ultimately be matched with their engine
in the final vehicle product.
    While we agree that these concerns are valid, they can also be said
of the

under 14,000 pound applications (except perhaps the tank size concern).
The over 14,000 pound gasoline applications are expected to use near
identical, if not equivalent, evaporative system components and we are
not aware of any reason why the existing monitoring techniques would
not continue to work on over 14,000 pound applications. Nonetheless, we
do not want false failures in the field. By limiting the monitoring
requirement to leaks of 0.150 inch or larger, we believe that
manufacturers would be able to employ a single monitoring strategy to
all possible tank sizes and configurations without much concern for
false failures. Nonetheless, it may be necessary for manufacturers to
impose tighter restrictions on their engine purchasers than is done
currently with regards to tank specifications and evaporative system
components.
8. Exhaust Gas Sensor Monitoring
    Our light-duty OBD requirements since the 1996 model year and our
8,500 to 14,000 pound OBD requirements since the 2005 model year have
required oxygen sensor monitoring similar to the requirements being
proposed. Years of compliance with those requirements demonstrates the
technological feasibility of the proposed requirements. Additionally,
A/F sensor monitoring has been required and demonstrated on these
vehicles for many years.

C. Feasibility of the Monitoring Requirements for Other Diesel and
Gasoline Systems

1. Variable Valve Timing and/or Control (VVT) System Monitoring
    VVT systems are already in general use in many under 14,000 pound
applications. Further, under the California OBD II requirements,
vehicles equipped with VVT systems have been monitoring those systems
for proper function since the 1996 model year. More recently,
manufacturers have employed monitoring strategies to detect VVT system
malfunctions that detect not only proper function but also exceedances
of emissions thresholds. Such strategies include the use of the crank
angle sensor and camshaft position sensor to confirm that the valve
opening and closing occurs within an allowable tolerance of the
commanded crank angle. By calculating the difference between the
commanded valve opening crank angle and the achieved valve opening
crank angle, a diagnostic algorithm can differentiate between a
malfunctioning system with too large of an error and a properly
functioning system with very little to no error. By calibrating the
size of this error (or integrating it over time), manufacturers can
design the system to indicate a malfunction prior to the required
emissions thresholds. In the same manner, system response can be
measured by monitoring the length of time necessary to achieve the
commanded valve timing. To ensure adequate resolution between properly
functioning systems and malfunctioning systems, most manufacturers
perform this type of monitor only when a sufficiently large ``step
change'' in commanded valve timing occurs.
2. Engine Cooling System Monitoring
    The existing OBD requirements have required identical ECT sensor
and thermostat monitoring for several years. While the technical
feasibility of the proposed requirements has been demonstrated on
lighter applications which tend to be produced through a vertically
integrated manufacturing process, the manufacturers of big diesel
engines have expressed concerns that monitoring of the cooling system
on over 14,000 pound applications would create unique and possibly
insurmountable challenges. Generally, the cooling system is divided
into two cooling circuits connected by the thermostat. The two circuits
are the engine circuit and the radiator circuit. Since the big diesel
engine industry tends to be horizontally integrated, the manufacturers
contend that they do not know what types of devices will be added to
the cooling system when the vehicle is manufactured or the vehicle is
put into service. They are concerned that the unknown devices can add/
remove unknown quantities of heat to/from the system which would
prevent them from predicting reliably the proper system behavior (e.g.,
warm up). Without the ability to predict system behavior reliably, they
fear that they cannot know when the system is malfunctioning (e.g., not
warming up as expected).
    The industry's concerns regarding unknown devices added on the
radiator circuit of the system seem unwarranted. A properly functioning
thermostat does not allow flow through the radiator during warm-up.
Devices added to the radiator circuit could only affect coolant
temperature when there is significant coolant flow through the radiator
(i.e., after the engine is warmed-up and the thermostat is open,
allowing coolant to flow through the radiator).
    We agree that unknown devices added on the engine circuit (e.g.,
passenger compartment heaters) can affect the warm-up rate of the
system. Manufacturers of under 14,000 pound applications have
demonstrated robust thermostat monitoring with high capacity passenger
heaters in the cooling system. To do so, they have to know the maximum
rate of heat loss due to the heater. Manufacturers of over 14,000 pound
applications have control over this by providing limits on such devices
in the build specifications that they provide to the vehicle
manufacturers. In some cases, an engine manufacturer might need
multiple build specifications with corresponding thermostat monitoring
calibrations to accommodate the ranges of heater capacities that are
needed when a given engine is used in a range of vehicle applications
(e.g., a local delivery truck having a passenger compartment for two
people and a small capacity heater versus a bus having a passenger
compartment for 20 people and a large capacity heater). The vehicle
manufacturer would then select the appropriate calibration for the
engine when installing it in the vehicle. Nonetheless, engine
manufacturers have requested limited enable conditions for the
thermostat monitor (e.g., to disable the thermostat monitor below 50
degrees F). This would help to minimize their resource needs to
calibrate the thermostat monitor. While this may be directionally
favorable to manufacturers, it would result in disabled thermostat
monitoring during cold ambient conditions which occur in much of the
country and, in some areas, during a large portion of the year. In such
regions, a vehicle could experience a thermostat malfunction with no
indication to the vehicle operator. Since many other OBD monitors will
operate only after reaching a certain engine coolant temperature, a
malfunctioning thermostat without any indication could effectively
result in disablement of the OBD system.
3. Crankcase Ventilation System Monitoring
    Crankcase ventilation system monitoring requirements have been met
for years by manufacturers of under 14,000 pound gasoline applications.
Therefore, the technological feasibility has been demonstrated for
gasoline applications.
    Effectively, diesel engine manufacturers would be required to meet
design requirements for the entire system in lieu of actually
monitoring any of the hoses for disconnection. Specifically, the
proposed requirement would allow for an exemption for any portion of
the system that is resistant to deterioration or accidental
disconnection and not subject to disconnection during any of the

manufacturer's repair procedures for non-crankcase ventilation system
repair work. These safeguards would be expected to eliminate the
chances of disconnected or improperly connected hoses while still
allowing manufacturers to meet the requirements without adding any
additional hardware meant solely for the purpose of meeting the
monitoring requirements.
4. Comprehensive Component Monitoring
    Both ARB and EPA OBD requirements have for year contained
requirements to monitor computer input and output components. While
these monitors are sometimes tricky and are not easy as many
incorrectly assume, the many years of successful implementation and
compliance with the existing requirements demonstrates their
feasibility. The proposed requirements are equivalent to the under
14,000 pound requirements.

IV. What Are the Service Information Availability Requirements?

A. What Is the Important Background Information for the Proposed
Service Information Provisions?

    Section 202(m)(5) of the CAA directs EPA to promulgate regulations
requiring OEMs to provide to:

any person engaged in the repairing or servicing of motor vehicles
or motor vehicle engines, and the Administrator for use by any such
persons, * * * any and all information needed to make use of the
[vehicle's] emission control diagnostic system * * * and such other
information including instructions for making emission-related
diagnoses and repairs.

    Such requirements are subject to the requirements of section 208(c)
regarding protection of trade secrets; however, no such information may
be withheld under section 208(c) if that information is provided
(directly or indirectly) by the manufacturer to its franchised dealers
or other persons engaged in the repair, diagnosing or servicing of
motor vehicles.
    On June 27, 2003 EPA published a final rulemaking (68 FR 38428)
which set forth the Agency's service information regulations for light-
and heavy-duty vehicles and engines below 14,000 pounds GVWR. These
regulations, in part, required each-covered Original Equipment
Manufacturer (OEM) to do the following: (1) OEMs must make full text
emissions-related service information available via the World Wide Web.
(2) OEMs must provide equipment and tool companies with information
that allows them to develop pass-through reprogramming tools. (3) OEMs
must make available enhanced diagnostic information to equipment and
tool manufacturers and to make available OEM-specific diagnostic tools
for sale. These requirements were finalized to ensure that aftermarket
service and repair facilities have access to the same emission-related
service information, in the same or similar manner, as that provided by
OEMs to their franchised dealerships.
    As EPA moves forward proposing OBD requirements for the heavy-duty
over 14,000 pounds sector, EPA is similarly moving forward with
proposals to require the availability of service information to heavy-
duty aftermarket service providers as required by section 202(m) of the
Clean Air Act.
    All of the following proposed provisions regarding the availability
of service information for the heavy-duty industry are based on our
extensive experience and regulatory history with the light-duty service
industry. However, as discussed below, EPA understands that there may
be significant differences between the light-duty service industry and
the heavy-duty service industry. EPA welcomes comment on all of the
proposed provisions and their need and/or applicability to the heavy-
duty service industry.
B. How Do the Below 14,000 Pound and Above 14,000 Pounds Aftermarket
Service Industry Compare?
    As we consider proposing the availability of service information
for the heavy-duty sector above 14,000 pounds, EPA recognizes that
differences do exist between the industries that service vehicles above
and below 14,000 pounds. On the below 14,000 pound side, estimates
indicate that independent technicians perform up to 80% of all vehicle
service and repairs once a vehicle exceeds the manufacturer warranty
period.\69\ On the above 14,000 pound side, the 1997 U.S. Census Bureau
Vehicle Inventory and Use Survey, estimated that 25 percent of the
general maintenance and over 30 percent of the major overhaul on heavy-
duty vehicles was performed by the independent sector. According to the
Census Bureau, these values represent a 16.7 percent increase in
general maintenance and a 6.2 percent increase in major overhaul from
1992. Trucks and Parts Service Magazine provides the following
information on the breakdown of the independent repair industry for
vehicles above 14,000 pounds (not including any fuel injection shops):
---------------------------------------------------------------------------

    \69\ Motor and Equipment Manufacturers Association, Automotive
Industry Status Report, 1999.

U.S. independent machine shops for above 14,000 pounds--5,820
U.S. independent engine service shops for above 14,000 pounds--12,170
U.S. independent transmission repair shops for above 14,000 pounds--
11,420
Technicians, independent repair shops for above 14,000 pounds--133,700
Technicians, truck parts distributors for vehicles above 14,000
pounds--41,600

    Thus, the increase in business and the large number of independent
aftermarket shops make it necessary that repair information is readily
available for the aftermarket trucking industry.
    On the light-duty side, vehicle manufacturers are entirely
integrated in that they are responsible for the design and production
of the entire vehicle from the chassis to the body. In comparison, the
heavy-duty industry is mostly non-integrated. In other words, different
manufacturers separately produce the engine, the chassis, and the
transmission of a vehicle. This non-integration speaks to the fact that
a completed vehicle is typically produced in response to the customized
needs of owners/operators. In addition, the lack of integration
indicates that a given engine will ultimately be part of many different
engine, transmission, and chassis configurations. In addition, heavy-
duty manufacturers have stated that diagnostic tool designs differ
significantly from tools produced for light-duty vehicles as a result
of this non-integration.
    EPA requests comment and also additional data on the current state
of the heavy-duty aftermarket industry.

C. What Provisions Are Being Proposed for Service Information
Availability?

1. What Information Is Proposed To Be Made Available by OEMs?
    Today's action proposes a provision that requires OEMs to make
available to any person engaged in the repairing or servicing of heavy-
duty motor vehicles or motor vehicle engines above 14,000 pounds all
information necessary to make use of the OBD systems and any
information for making emission-related repairs, including any
emissions-related information that is provided by the OEM to franchised
dealers beginning with MY2010. We are proposing that this information
includes, but is not limited to, the following:
    (1) Manuals, technical service bulletins (TSBs), diagrams, and
charts (the provisions for training materials,

including videos and other media are discussed in Sections II.C.3 and
II.C.4 below.
    (2) A general description of the operation of each monitor,
including a description of the parameter that is being monitored.
    (3) A listing of all typical OBD diagnostic trouble codes
associated with each monitor.
    (4) A description of the typical enabling conditions for each
monitor to execute during vehicle operation, including, but not limited
to, minimum and maximum intake air and engine coolant temperature,
vehicle speed range, and time after engine startup. A listing and
description of all existing monitor-specific drive cycle information
for those vehicles that perform misfire, fuel system, and comprehensive
component monitoring.
    (5) A listing of each monitor sequence, execution frequency and
typical duration.
    (6) A listing of typical malfunction thresholds for each monitor.
    (7) For OBD parameters that deviate from the typical parameters,
the OBD description shall indicate the deviation for the vehicles it
applies to and provide a separate listing of the typical values for
those vehicles.
    (8) Identification and scaling information necessary to interpret
and understand data available to a generic scan tool through Diagnostic
Message 8 pursuant to SAE Recommended Practice J1939-73, which is
incorporated by reference in section X.
    (9) For vehicles below 14,000 pounds, EPA requires that any
information related to the service, repair, installation or replacement
of parts or systems developed by third party (Tier 1) suppliers for
OEMs, to the extent they are made available to franchise dealerships.
EPA believes that Tier 1 suppliers are an important element of the
market related to vehicles below 14,000 pounds and EPA is requesting
comment on the role that Tier 1 suppliers play in the heavy-duty market
above 14,000 pounds and the need to extend this provision to the heavy-
duty industry above 14,000 pounds.
    (10) Any information on other systems that can directly effect the
emission system within a multiplexed system (including how information
is sent between emission-related system modules and other modules on a
multiplexed bus),
    (11) Any information regarding any system, component, or part of a
vehicle monitored by the OBD system that could in a failure mode cause
the OBD system to illuminate the malfunction indicator light (MIL).
    (12) Any other information relevant to the diagnosis and completion
of an emissions-related repair. This information includes, but is not
limited to, information needed to start the vehicle when the vehicle is
equipped with an anti-theft or similar system that disables the engine
described below in paragraph (13). This information also includes any
OEM-specific emissions-related diagnostic trouble codes (DTCs) and any
related service bulletins, trouble shooting guides, and/or repair
procedures associated with these OEM-specific DTCs.
    (13) For vehicles below 14,000 pounds, EPA requires that OEMs make
available computer or anti-theft system initialization information
necessary for the proper installation of on-board computers on motor
vehicles that employ integral vehicle security systems or the repair or
replacement of any other emission-related part. We did not finalize a
provision that would require OEMs to make this information available on
the OEM's Web site unless they chose to do so. However, we did finalize
a provision requiring that the OEM's Web site contain information on
alternate means for obtaining the information and/or ability to perform
reintialization. EPA is proposing to expand this provision to OEMs for
vehicles above 14,000 pounds and requests comment on the prevalence of
this type of repair, the means and methods for performing this type of
repair and the need to extend this provision to the heavy-duty
industry.
    In addition, EPA's current service information rules require that,
beginning with the 2008 model year, all OEM systems will be designed in
such a way that no special tools or processes will be necessary to
perform re-initialization. In other words, EPA expects that the re-
initialization of vehicles can be completed with generic aftermarket
tools, a pass-through device, or an inexpensive OEM-specific cable. EPA
finalized this provision for vehicles below 14,000 pounds to prevent
the need for aftermarket service providers to invest in expensive OEM-
specific or specialty tools to complete an emissions-related repair
that does not occur very frequently, but does in fact occur. In the
June 2003 final rule, EPA gave OEMs a significant amount of lead time
to either separate the need for reinitialization from an emissions
related repair or otherwise redesign the reinitialization process in