of the boost pressure system--e.g., control of VGT position, turbine
speed, manifold pressure--the OBD system shall detect a malfunction
when and if:
     The system fails to begin feedback control within a
manufacturer specified time interval;
     A failure or deterioration causes open loop or default
operation; or
     Feedback control has used up all of the adjustment allowed
by the manufacturer.
v. Charge Air Undercooling Malfunctions
    We are proposing that the OBD system detect a malfunction of the
charge air cooling system prior to a decrease from the manufacturer's
specified cooling rate that would cause an engine's emissions to exceed
the emissions thresholds for ``other monitors'' as shown in Table II.B-
1. For engines in which no failure or deterioration of the charge air
cooling system that causes a decrease in cooling performance could
result in an engine's emissions exceeding the applicable emissions
thresholds, the OBD system must detect a malfunction when the system
has no detectable amount of charge air cooling.
c. Turbo Boost Control System Monitoring Conditions
    We are proposing that the OBD system monitor continuously for
underboost and overboost malfunctions and for boost feedback control
malfunctions. Manufacturers would be required to define the monitoring
conditions for VGT slow response malfunctions such that the minimum
performance ratio requirements discussed in section II.E would be met
with the exception that monitoring must occur every time the monitoring
conditions are met during the driving cycle in lieu of once per driving
cycle as required for most monitors. For purposes of tracking and
reporting as required in section II.E, all monitors used to detect VGT
slow response malfunctions malfunctions must be tracked separately but
reported as a single set of values as discussed in section II.E.\20\
---------------------------------------------------------------------------

    \20\ For specific components or systems that have multiple
monitors that are required to be reported (e.g., exhaust gas sensor
bank 1 may have multiple monitors for sensor response or other
sensor characteristics), the OBD system must separately track
numerators and denominators for each of the specific monitors and
report only the corresponding numerator and denominator for the
specific monitor that has the lowest numerical ratio. If two or more
specific monitors have identical ratios, the corresponding numerator
and denominator for the specific monitor that has the highest
denominator shall be reported for the specific component.
---------------------------------------------------------------------------

d. Turbo Boost MIL Illumination and DTC Storage
    We are proposing the general MIL illumination and DTC storage
requirements as discussed in section II.A.2.
5. Non-Methane Hydrocarbon (NMHC) Converting Catalyst Monitoring
a. Background
    Diesel oxidation catalysts (DOCs) have been used on some nonroad
diesel engines since the 1960s and on some diesel trucks and buses in
the U.S. since the early 1990s. DOCs are generally used for converting
HC and carbon monoxide (CO) emissions to water and CO2 via
an oxidation process. Current DOCs can also be used to convert PM
emissions. DOCs may also be used in conjunction with other
aftertreatment emission controls--such as NOX adsorber
systems, selective catalytic reduction (SCR) systems, and PM filters--
to improve their performance and/or clean up certain reducing agents
that might slip through the system (e.g., the urea used in urea SCR
systems).
b. NMHC Converting Catalyst Monitoring Requirements
    We are proposing that the OBD system monitor the NMHC converting
catalyst(s) for proper NMHC conversion capability. We are also
proposing that each catalyst that converts NMHC be monitored either
individually or in combination with others. For engines equipped with
catalyzed diesel particulate filters (CDPFs) that convert NMHC
emissions, the catalyst function of the CDPF must be monitored in
accordance with the CDPF monitoring requirements in section II.B.8.
i. NMHC Converting Catalyst Conversion Efficiency
    We are proposing that the OBD system detect an NMHC catalyst
malfunction when the catalyst conversion capability decreases to the
point that NMHC emissions exceed the emissions thresholds for ``NMHC
catalysts'' as shown in Table II.B-1. If no failure or deterioration of
the catalyst NMHC conversion capability could result in an engine's
NMHC emissions exceeding the applicable emissions thresholds, the OBD
system would have to detect a malfunction when the catalyst has no
detectable amount of NMHC conversion capability.
ii. Other Aftertreatment Assistance Functions
    For catalysts used to generate an exotherm to assist CDPF
regeneration, we are proposing that the OBD system detect a malfunction
when the catalyst is unable to generate a sufficient exotherm to
achieve that regeneration. For catalysts used to generate a feedgas
constituency to assist SCR systems (e.g., to increase NO2
concentration upstream of an SCR system), the OBD system would have to
detect a malfunction when the catalyst is unable to generate the
necessary feedgas constituents for proper SCR system operation. For
catalysts located downstream of a CDPF and used to convert NMHC
emissions during a CDPF regeneration event, the OBD system would be
required to detect a malfunction when the catalyst has no detectable
amount of NMHC conversion capability.
c. NMHC Converting Catalyst Monitoring Conditions
    Manufacturers would be required to define the monitoring conditions
for NMHC converting catalyst malfunctions such that the minimum
performance ratio requirements discussed in section II.E would be met.
For purposes of tracking and reporting as discussed in section II.E,
all monitors used to detect NMHC converting catalyst malfunctions must
be tracked separately but reported as a single set of values as
discussed in section II.E.\21\
---------------------------------------------------------------------------

    \21\ For specific components or systems that have multiple
monitors that are required to be reported (e.g., exhaust gas sensor
bank 1 may have multiple monitors for sensor response or other
sensor characteristics), the OBD system must separately track
numerators and denominators for each of the specific monitors and
report only the corresponding numerator and denominator for the
specific monitor that has the lowest numerical ratio. If two or more
specific monitors have identical ratios, the corresponding numerator
and denominator for the specific monitor that has the highest
denominator shall be reported for the specific component.
---------------------------------------------------------------------------

d. NMHC Converting Catalyst MIL Illumination and DTC Storage
    We are proposing the general requirements for MIL illumination and
DTC storage discussed in section II.A.2. Note that the monitoring
method for the catalyst(s) must be capable of detecting all instances,
except diagnostic self-clearing, when a catalyst DTC has been cleared
but the catalyst has not been replaced (e.g., catalyst over temperature
histogram approaches are not acceptable).\22\
---------------------------------------------------------------------------

    \22\ For gasoline catalyst monitoring, manufacturers generally
use what is called an exponentially weighted moving average (EWMA)
approach to making decisions about the catalyst's pass/fail status.
This approach monitors the catalyst and ``saves'' that information.
The next time it monitors the catalyst, it saves that information
along with the previous information, placing a higher weighting on
the most recent information. This is done every time the OBD system
monitors the catalyst and the EWMA saves six or seven monitoring
events before making a decision. Importantly, once there exists six
or seven pieces of information, every monitoring event can result in
a decision because the EWMA is always using the previous six or
seven events. Unfortunately, if a service technician clears the data
with a scan tool, it is going to take six or seven monitoring events
before the catalyst monitor can make a decision on the pass/fail
status of the catalyst. So, we want to be sure that, in addition to
the EWMA aspect of the catalyst monitor, there exists a way of
determining quickly that someone has cleared the data but perhaps
did not actually repair the catalyst. This is required to help
prevent against DTC clearing without fixing a failed catalyst as a
means of passing an inspection & maintenance test.

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

6. Selective Catalytic Reduction (SCR) and Lean NOX Catalyst
Monitoring
a. Background
    Selective Catalytic Reduction (SCR) catalysts that use ammonia as a
NOX reductant have been used for stationary source
NOX control for a number of years. Frequently, urea is used
as the source of ammonia for SCR catalysts, and such systems are
commonly referred to as Urea SCR systems. In recent years, considerable
effort has been invested in developing urea SCR systems that could be
applied to heavy-duty diesel vehicles with low sulfur diesel fuel. We
now expect that urea SCR systems will be introduced in Europe to comply
with the EURO IV heavy-duty diesel emission standards. Such systems
have been introduced in the past year by some heavy-duty diesel engine
manufacturers both in Europe and in Japan.
    SCR catalyst systems require an accurate urea control system to
inject precise amounts of reductant. An injection rate that is too low
may result in lower NOX conversions while an injection that
is too high may release unwanted ammonia emissions--referred to as
ammonia slip--to the atmosphere. In general, ammonia to NOX
ratios of around 1:1 are used to provide the highest NOX
conversion rates with minimal ammonia slip. Therefore, injecting just
the right amount of ammonia appropriate for the amount of
NOX in the exhaust is very important. This can be
challenging in a highway application because on-road diesel engines
operate over a variety of speeds and loads. This makes the use of
closed-loop feedback systems for reductant metering very attractive.
This can be achieved, for example, with a dedicated NOX
sensor in the exhaust so that the NOX concentration can be
accurately known. With an accurate fast response NOX sensor,
closed-loop control of the ammonia injection can be used to achieve and
maintain the desired ammonia/NOX ratios in the SCR catalyst
for the high NOX conversion efficiencies necessary to
achieve the 2010 emission standards under various engine operating
conditions.
    Some have estimated that achieving the 2010 NOX emission
standards with SCR systems will require NOX sensors that can
measure NOX levels accurately in the 20 to 40 ppm range with
little cross sensitivity to ammonia. Some in industry have even stated
a desire for accuracy in the two to three ppm range. Suppliers have
been developing NOX sensors capable of measuring
NOX in the 0 to 100 ppm range with +/-5 ppm accuracy which
we believe will be available by 2010.\23\ Regarding cross-sensitivity
to ammonia, work has been done that indicates ammonia and
NOX measurements can be independently measured by
conditioning the output signal.\24\ This signal conditioning method
resulted in a linear output for both ammonia and NOX from
the NOX sensor downstream of the catalyst.
---------------------------------------------------------------------------

    \23\ Draft Technical Support Document, HDOBD NPRM, EPA420-D-06-
006, Docket ID EPA-HQ-OAR-2005-0047-0008.
    \24\ 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.
---------------------------------------------------------------------------

    For SCR systems, closed-loop control of the reductant injection may
require the use of two NOX sensors. The first NOX
sensor would be located upstream of the catalyst and the reductant
injection point would be used for measuring the engine-out
NOX emissions and determining the amount of reductant
injection needed to reduce emissions. The second NOX sensor
located downstream of the catalyst would be used for measuring the
amount of ammonia and NOX emissions exiting the catalyst and
providing feedback to the reductant injection control system. If the
downstream NOX sensor detects too much NOX
emissions exiting the catalyst, the control system can inject higher
quantities of reductant. Conversely, if the downstream NOX
sensor detects too much ammonia slip exiting the catalyst, the control
system can decrease the amount of reductant injection.
    In addition to exhaust NOX levels, another important
parameter for achieving high NOX conversion rates with
minimum ammonia slip is catalyst temperature. SCR catalysts have a
defined temperature range where they are most effective. For example,
platinum catalysts are effective between 175 and 250 degrees Celsius,
vanadium catalysts are effective between 300 and 450 degrees Celsius,
and zeolite catalysts are most effective between 350 and 600 degrees
Celsius. To determine exhaust catalyst temperature for reductant
control purposes, manufacturers are likely to use temperature sensors
placed in the exhaust system. We project that only one temperature
sensor positioned just downstream of the SCR system will be utilized
for reductant injection control purposes.
    Production SCR catalyst systems may also contain auxiliary
catalysts to improve the overall emissions control capability of the
system. An oxidation catalyst is often positioned downstream of the SCR
catalyst to help control ammonia slip on systems without closed-loop
control of ammonia injection. The use of a ``guard'' catalyst could
allow higher ammonia injection levels, thereby increasing the
NOX conversion efficiency without releasing un-reacted
ammonia into the exhaust. The guard catalyst can also reduce HC and CO
emission levels and diesel odors. However, increased N2O emissions may
occur and NOX emission levels may actually increase if too
much ammonia is oxidized in the catalyst. Some SCR systems may also
include an oxidation catalyst upstream of the SCR catalyst and urea
injection point to generate NO2 for lowering the effective operating
temperature and/or volume of the SCR catalyst. Studies have indicated
that increasing the NO2 content in the exhaust stream can reduce the
SCR temperature requirements by about 100 degrees Celsius.\25\ This
``pre-oxidation'' catalyst also has the added benefit of reducing HC
emissions.
---------------------------------------------------------------------------

    \25\ Walker, A. P., Chandler, G. R., Cooper, B. J., et al., ``An
Integrated SCR and Continuously Regenerating Trap System to Meet
Future NOX and PM Legislation,'' SAE Paper 2000-01-0188
which may be obtained from Society of Automotive Engineers
International, 400 Commonwealth Dr., Warrendale, PA, 15096-0001.
---------------------------------------------------------------------------

b. SCR and Lean NOX Catalyst Monitoring Requirements
    We are proposing that the OBD system monitor SCR catalysts and lean
NOX catalysts for proper conversion capability. We are also
proposing that each catalyst that converts NOX be monitored
either individually or in combination with others. For engines equipped
with SCR systems or other catalyst systems that utilize an active/
intrusive reductant injection (e.g., active lean NOX
catalysts utilizing diesel fuel

injection), the OBD system would be required to monitor the active/
intrusive reductant injection system for proper performance. The
individual electronic components (e.g., actuators, valves, sensors,
heaters, pumps) in the active/intrusive reductant injection system must
be monitored in accordance with the comprehensive component
requirements in section II.D.4.
i. Catalyst Conversion Efficiency Malfunctions
    We are proposing that the OBD system detect a catalyst malfunction
when the catalyst conversion capability decreases to the point that
would cause an engine's NOX emissions to exceed any of the
applicable emissions thresholds for ``NOX Catalyst Systems''
as shown in Table II.B-1. If no failure or deterioration of the
catalyst NOX conversion capability could result in an
engine's NOX emissions exceeding any of the applicable
emissions thresholds, the OBD system would have to detect a malfunction
when the catalyst has no detectable amount of NOX conversion
capability.
ii. Active/Intrusive Reductant Injection System Malfunctions
    Specific to SCR and other active/intrusive reductant injection
system performance, we are proposing that the OBD system detect a
malfunction prior to any failure or deterioration of the system to
regulate reductant delivery properly (e.g., urea injection, separate
injector fuel injection, post injection of fuel, air assisted
injection/mixing) that would cause an engine's NOX emissions
to exceed any of the applicable emissions thresholds for
``NOX Catalyst Systems'' as shown in Table II.B-1. As above,
if no failure or deterioration of the reductant delivery system could
result in an engine's NOX emissions exceeding the applicable
emissions thresholds, the OBD system would have to detect a malfunction
when the system has reached its control limits such that it is no
longer able to deliver the desired quantity of reductant.
    If the system uses a reductant other than the fuel used for the
engine or uses a reservoir/tank for the reductant that is separate from
the fuel tank used for the engine, the OBD system must detect a
malfunction when there is no longer sufficient reductant available
(e.g., the reductant tank is empty). If the system uses a reservoir/
tank for the reductant that is separate from the fuel tank used for the
engine, the OBD system must detect a malfunction when an improper
reductant is used in the reductant reservoir/tank (e.g., the reductant
tank is filled with something other than the proper reductant).
iii. SCR and Lean NOX Catalyst Feedback Control System
Malfunctions
    If the engine is equipped with feedback control of the reductant
injection, we are proposing that the OBD system detect a malfunction
when and if:
     The system fails to begin feedback control within a
manufacturer specified time interval;
     A failure or deterioration causes open loop or default
operation; or
     Feedback control has used up all of the adjustment allowed
by the manufacturer.
c. SCR and Lean NOX Catalyst Monitoring Conditions
    Manufacturers would be required to define the monitoring conditions
for catalyst conversion efficiency malfunctions such that the minimum
performance ratio requirements discussed in section II.E would be met.
For purposes of tracking and reporting as required in section II.E, all
monitors used to detect catalyst conversion efficiency malfunctions
must be tracked separately but reported as a single set of values as
specified in section II.E.\26\ We are also proposing that the OBD
system monitor continuously for active/intrusive reductant injection
system malfunctions. Manufacturers would be required to monitor
continuously the active/intrusive reductant delivery system.
---------------------------------------------------------------------------

    \26\ For specific components or systems that have multiple
monitors that are required to be reported (e.g., exhaust gas sensor
bank 1 may have multiple monitors for sensor response or other
sensor characteristics), the OBD system must separately track
numerators and denominators for each of the specific monitors and
report only the corresponding numerator and denominator for the
specific monitor that has the lowest numerical ratio. If two or more
specific monitors have identical ratios, the corresponding numerator
and denominator for the specific monitor that has the highest
denominator shall be reported for the specific component.
---------------------------------------------------------------------------

d. SCR and Lean NOX Catalyst MIL Illumination and DTC
Storage
    We are proposing the general MIL illumination and DTC storage
requirements presented in section II.A.2 with the exception of active/
intrusive reductant injection related malfunctions. If the OBD system
is capable of discerning that a system malfunction is being caused by
an empty reductant tank, the manufacturer may delay illumination of the
MIL if the vehicle is equipped with an alternative indicator for
notifying the vehicle operator of the malfunction. The manufacturer
would be required to demonstrate that: The alternative indicator is of
sufficient illumination and location to be readily visible to the
operator under all lighting conditions; and the alternative indicator
provides equivalent assurance that a vehicle operator will be promptly
notified; and, that corrective action would be undertaken. If the
vehicle is not equipped with an alternative indicator and the MIL
illuminates, the MIL may be immediately extinguished and the
corresponding DTC erased once the OBD system has verified that the
reductant tank has been properly refilled and the MIL has not been
illuminated for any other type of malfunction. The Administrator may
approve other strategies that provide equivalent assurance that a
vehicle operator will be promptly notified and that corrective action
will be undertaken.
    The monitoring method for the catalyst(s) would have to be capable
of detecting all instances, except diagnostic self-clearing, when a
catalyst DTC has been cleared but the catalyst has not been replaced
(e.g., catalyst over temperature histogram approaches are not
acceptable).
7. NOX Adsorber System Monitoring
a. Background
    NOX adsorbers, or lean NOX traps (LNT), work
to control NOX emissions by storing NOX on the
surface of the catalyst during the lean engine operation typical of
diesel engines and then by undergoing subsequent brief rich
regeneration events where the NOX is released and reduced
across a precious metal catalyst.
    NOX adsorber systems generally consist of a conventional
three-way catalyst function (e.g., platinum) with NOX
storage components (i.e., adsorbents) incorporated into the washcoat.
Three-way catalysts convert NOX emissions as well as HC and
CO emissions (hence the name three-way) by promoting oxidation of HC
and CO to H2O and CO2 using the oxidation
potential of the NOX pollutant and, in the process, reducing
the NOX emissions to nitrogen, N2. Said another
way, three-way catalysts work with exhaust conditions where the net
oxidizing and reducing chemistry of the exhaust is approximately equal,
allowing the catalyst to promote complete oxidation/reduction reactions
to the desired exhaust components of CO2, H2O,
and N2. The oxidizing potential in the exhaust comes from
NOX emissions and any feedgas oxygen (O2) not
consumed during combustion. The reducing potential in the exhaust

comes from HC and CO emissions, which represent products of incomplete
combustion. Operation of the engine to ensure that the oxidizing and
reducing potential of the combustion and exhaust conditions is
precisely balanced is referred to as stoichiometric engine operation.
    Because diesel engines run lean of stoichiometric operation, the
NOX emissions are stored, or absorbed--via chemical reaction
with alkaline earth metals such as barium nitrate in the washcoat--and
then released during rich operation for conversion to N2.
This NOX release during rich operation is referred to as a
regeneration event. The rich operating conditions required for
NOX regeneration, which generally last for several seconds,
are typically achieved using a combination of intake air throttling (to
reduce the amount of intake air), exhaust gas recirculation, and post-
combustion fuel injection.
    NOX adsorber systems have demonstrated NOX
reduction efficiencies from 50 percent to in excess of 90 percent. This
efficiency has been found to be highly dependent on the fuel sulfur
content because NOX adsorbers are extremely sensitive to
sulfur. The NOX adsorption material has an even greater
affinity for sulfur compounds than NOX. Thus, sulfur
compounds can saturate the adsorber and limit the number of active
sites for NOX adsorption, thereby lowering the
NOX reduction efficiency. Accordingly, low sulfur fuel is
required to achieve the greatest NOX reduction efficiencies.
Although new adsorber washcoat materials are being developed with a
higher resistance to sulfur poisoning and ultra-low sulfur fuel will be
the norm by 2010, NOX adsorber systems will still need to
purge the stored sulfur from the storage bed by a process referred to
as desulfation. Because the desulfation process takes longer (e.g.,
several minutes) and requires more fuel and heat than the
NOX regeneration step, permanent thermal degradation of the
NOX adsorber and fuel economy penalties may result from
desulfation events happening with excessive frequency. However, if
desulfation is not done frequently enough, NOX storage
capacity would be compromised and fuel economy penalties would be
incurred from excessive attempts at NOX regeneration.
    In order to achieve and maintain high NOX conversion
efficiencies while limiting negative impacts on fuel economy and
driveability, vehicles with NOX adsorber systems will
require precise air/fuel control in the engine and in the exhaust
stream. Diesel manufacturers are expected to utilize NOX
sensors and temperature sensors to provide the most precise closed-loop
control for the NOX adsorber system. If NOX
sensors are not used to control the NOX adsorber system,
manufacturers could use wide-range air-fuel (A/F) sensors located
upstream and downstream of the adsorber as a substitute. However, A/F
sensors cannot provide an instantaneous indication of tailpipe
NOX levels, which would allow the control system to
precisely determine when the adsorber system is filled to capacity and
regeneration should be initiated. If A/F sensors are used in lieu of
NOX sensors, an estimation of engine-out NOX
emissions and their subsequent storage in the NOX adsorber
can be achieved indirectly through modeling.
b. NOX Adsorber System Monitoring Requirements
    We are proposing that the OBD system monitor the NOX
adsorber on engines so equipped for proper performance. For engines
equipped with active/intrusive injection (e.g., in-exhaust fuel and/or
air injection) to achieve NOX regeneration, the OBD system
would have to monitor the active/intrusive injection system for proper
performance. The individual electronic components (e.g., injectors,
valves, sensors) that are used in the active/intrusive injection system
would have to be monitored in accordance with the comprehensive
component requirements in section II.D.4.
i. NOX Adsorber Capability Malfunctions
    We are proposing that the OBD system detect a NOX
adsorber malfunction when its capability--i.e., its combined adsorption
and conversion capability--decreases to the point that would cause an
engine's NOX emissions to exceed the applicable emissions
thresholds for ``NOX Catalyst Systems'' as shown in Table
II.B-1. If no failure or deterioration of the NOX adsorber
capability could result in an engine's NOX emissions
exceeding the applicable emissions thresholds, the OBD system would
have to detect a malfunction when the system has no detectable amount
of NOX adsorber capability.
ii. Active/Intrusive Reductant Injection System Malfunctions
    For NOX adsorber systems that use active/intrusive
injection (e.g., in-cylinder post fuel injection, in-exhaust air-
assisted fuel injection) to achieve desorption of the NOX
adsorber, the OBD system would have to detect a malfunction if any
failure or deterioration of the injection system's ability to properly
regulate injection causes the system to be unable to achieve desorption
of the NOX adsorber.
iii. NOX Adsorber Feedback Control System Malfunctions
    If the engine is equipped with feedback control of the reductant
injection (e.g., feedback control of injection quantity, time), we are
proposing that the OBD system detect a malfunction when and if:
     The system fails to begin feedback control within a
manufacturer specified time interval;
     A failure or deterioration causes open loop or default
operation; or
     Feedback control has used up all of the adjustment allowed
by the manufacturer.
c. NOX Adsorber System Monitoring Conditions
    We are proposing that manufacturers define the monitoring
conditions for NOX adsorber capability malfunctions such
that the minimum performance ratio requirements discussed in section
II.E would be met. For purposes of tracking and reporting as required
in section II.E, all monitors used to detect NOX adsorber
capability malfunctions must be tracked separately but reported as a
single set of values as specified in section II.E.\27\ We are also
proposing that the OBD system monitor continuously for active/intrusive
reductant injection and feedback control system malfunctions.
---------------------------------------------------------------------------

    \27\ For specific components or systems that have multiple
monitors that are required to be reported (e.g., exhaust gas sensor
bank 1 may have multiple monitors for sensor response or other
sensor characteristics), the OBD system must separately track
numerators and denominators for each of the specific monitors and
report only the corresponding numerator and denominator for the
specific monitor that has the lowest numerical ratio. If two or more
specific monitors have identical ratios, the corresponding numerator
and denominator for the specific monitor that has the highest
denominator shall be reported for the specific component.
---------------------------------------------------------------------------

d. NOX Adsorber System MIL Illumination and DTC Storage
    We are proposing the general requirements for MIL illumination and
DTC storage discussed in section II.A.2.
8. Diesel Particulate Filter (DPF) System Monitoring
a. Background
    Diesel particulate filters control diesel PM by capturing the soot
(solid carbon) portion of PM in a filter media, typically a ceramic
wall flow substrate, and then by oxidizing (burning) it in the oxygen-
rich atmosphere of diesel exhaust.\28\ In aggregate over a driving
cycle, the PM must be burned at a rate equal to or

greater than its accumulation rate, or the DPF will clog. Given low
sulfur diesel fuel (diesel fuel with a sulfur content of 15 ppm or
lower), highly active catalytic metals (e.g., platinum) can be used to
promote soot oxidation. This method of PM filter regeneration, called
passive regeneration, is the primary means of soot oxidation that we
project industry will use in 2007/2010.
---------------------------------------------------------------------------

    \28\ See ``Regulatory Impact Analysis: Heavy-Duty Engine and
Vehicle Standards and Highway Diesel Fuel Sulfur Control
Requirements;'' EPA420-R-00-026; December 2000 at Chapter III for a
more complete description of DPFs.
---------------------------------------------------------------------------

    The DPF technology has proven itself in tens of thousands of
retrofit applications where low sulfur diesel fuel is already
available. More than a million light-duty passenger cars in Europe now
have diesel particulate filters. DPFs are considered the most effective
control technology for the reduction of particulate emissions and can
typically achieve PM reductions in excess of 90 percent.
    In order to maintain the performance of the DPF and the engine, the
trapped PM must be periodically removed before too much particulate is
accumulated and exhaust backpressure reaches unacceptable levels. The
process of periodically removing accumulated PM from the DPF is known
as ``regeneration'' and is very important for maintaining low PM
emission levels. DPF regeneration can be passive (i.e., occur
continuously during regular operation of the filter), active (i.e.,
occur on a controlled, periodic basis after a predetermined quantity of
particulates have been accumulated), or a combination of the two. With
passive regeneration, the oxidizing catalyst material on the DPF
substrate serves to lower the temperature for oxidizing PM. This allows
the DPF to continuously oxidize trapped PM material during normal
driving. In contrast, active systems utilize an external heat source--
such as an electric heater or fuel burner--to facilitate DPF
regeneration. We are projecting that virtually all DPF systems will
have some sort of active regeneration mechanism as a backup mechanism
should operating conditions not be conducive for passive regeneration.
    One of the key considerations for a DPF regeneration control system
is the amount of soot quantity that is stored in the DPF (often called
soot loading). If too much soot is stored when regeneration is
activated, the soot can burn uncontrollably and DPF substrate could be
damaged via melting or cracking. Conversely, activating regeneration
when there is too little trapped soot will not ensure good combustion
propagation which would effectively waste the energy (fuel) used to
initiate the regeneration. Another important consideration in the
control system design is the fuel economy penalty involved with DPF
regeneration. Prolonged operation with high backpressures in the
exhaust and regenerations occurring too frequently are both detrimental
to fuel economy and DPF durability. Therefore, DPF system designers
will need to carefully balance the regeneration frequency with various
conflicting factors. To optimize the trap regeneration for these design
factors, the DPF regeneration control system is projected to
incorporate both pressure sensors and temperature sensors to model soot
loading and other phenomena.\29\ Through the information provided by
these sensors, designers can optimize the DPF for high effectiveness
and maximum durability while minimizing fuel economy and performance
penalties.
---------------------------------------------------------------------------

    \29\ Salvat, O., Marez, P., and Belot, G., ``Passenger Car
Serial Application of a Particulate Filter System on a Common Rail
Direct Injection Diesel Engine,'' SAE Paper 2000-01-0473 which may
be obtained from Society of Automotive Engineers International, 400
Commonwealth Dr., Warrendale, PA, 15096-0001.
---------------------------------------------------------------------------

b. DPF System Monitoring Requirements
    We are proposing that the OBD system monitor the DPF on engines so-
equipped for proper performance.\30\ For engines equipped with active
regeneration systems that utilize an active/intrusive injection (e.g.,
in-exhaust fuel injection, in-exhaust fuel/air burner), the OBD system
would have to monitor the active/intrusive injection system for proper
performance. The individual electronic components (e.g., injectors,
valves, sensors) that are used in the active/intrusive injection system
must be monitored in accordance with the comprehensive component
requirements in section II.D.4.
---------------------------------------------------------------------------

    \30\ Note that these requirements would also apply to a
catalyzed diesel particulate filter (CDPF). We use the more common
term DPF throughout this discussion.
---------------------------------------------------------------------------

i. PM Filtering Performance
    We are proposing that the OBD system detect a malfunction prior to
a decrease in the filtering capability of the DPF (e.g., cracking,
melting, etc.) that would cause an engine's PM emissions to exceed the
applicable emissions thresholds for ``DPF Systems'' as shown in Table
II.B-1. If no failure or deterioration of the PM filtering performance
could result in an engine's PM emissions exceeding the applicable
emissions thresholds, the OBD system would have to detect a malfunction
when no detectable amount of PM filtering occurs.
ii. DPF Regeneration Frequency Malfunctions--Too Frequent
    We are proposing that the OBD system detect a malfunction when the
DPF regeneration frequency increases from--i.e., occurs more often
than--the manufacturer's specified regeneration frequency to a level
such that it would cause an engine's NMHC emissions to exceed the
applicable emissions threshold for ``DPF Systems'' as shown in Table
II.B-1. If no such regeneration frequency exists that could cause NMHC
emissions to exceed the applicable emission threshold, the OBD system
would have to detect a malfunction when the PM filter regeneration
frequency exceeds the manufacturer's specified design limits for
allowable regeneration frequency.
iii. DPF Incomplete Regeneration Malfunctions
    We are proposing that the OBD system detect a regeneration
malfunction when the DPF does not properly regenerate under
manufacturer-defined conditions where regeneration is designed to
occur.
iv. DPF NMHC Conversion Efficiency Malfunctions
    We are proposing that, for any DPF that serves to convert NMHC
emissions, the OBD system must monitor the NMHC converting function of
the DPF and detect a malfunction when the NMHC conversion capability
decreases to the point that NMHC emissions exceed the NMHC threshold
for ``DPF Systems'' as shown in Table II.B-1. If no failure or
deterioration of the NMHC conversion capability could result in NMHC
emissions exceeding the applicable NMHC threshold, the OBD system would
have to detect a malfunction when the system has no detectable amount
of NMHC conversion capability.
v. DPF Missing Substrate Malfunctions
    We are proposing that the OBD system detect a malfunction if either
the DPF substrate is completely destroyed, removed, or missing, or if
the DPF assembly has been replaced with a muffler or straight pipe.
vi. DPF Active/Intrusive Injection System Malfunctions
    We are proposing that, for systems that utilize active/intrusive
injection (e.g., in-cylinder post fuel injection, in-exhaust air-
assisted fuel injection) to achieve DPF regeneration, the OBD system
detect a malfunction if any

failure or deterioration of the injection system's ability to properly
regulate injection causes the system to be unable to achieve DPF
regeneration.
vii. DPF Regeneration Feedback Control System Malfunctions
    We are proposing that, if the engine is equipped with feedback
control of the DPF regeneration (e.g., feedback control of oxidation
catalyst inlet temperature, PM filter inlet or outlet temperature, in-
cylinder or in-exhaust fuel injection), the OBD system must detect a
malfunction when and if:
     The system fails to begin feedback control within a
manufacturer specified time interval;
     A failure or deterioration causes open loop or default
operation; or
     Feedback control has used up all of the adjustment allowed
by the manufacturer.
c. DPF System Monitoring Conditions
    We are proposing that manufacturers define the monitoring
conditions for all DPF related malfunctions such that the minimum
performance ratio requirements discussed in section II.E would be met
with the exception that monitoring must occur every time the monitoring
conditions are met during the driving cycle rather than once per
driving cycle as required for most monitors. For purposes of tracking
and reporting as required in section II.E, all monitors used to detect
all DPF related malfunctions would have to be tracked separately but
reported as a single set of values as specified in section II.E.\31\
---------------------------------------------------------------------------

    \31\ For specific components or systems that have multiple
monitors that are required to be reported (e.g., exhaust gas sensor
bank 1 may have multiple monitors for sensor response or other
sensor characteristics), the OBD system must separately track
numerators and denominators for each of the specific monitors and
report only the corresponding numerator and denominator for the
specific monitor that has the lowest numerical ratio. If two or more
specific monitors have identical ratios, the corresponding numerator
and denominator for the specific monitor that has the highest
denominator shall be reported for the specific component.
---------------------------------------------------------------------------

d. DPF System MIL Illumination and DTC Storage
    We are proposing the general requirements for MIL illumination and
DTC storage as discussed in section II.A.2.
9. Exhaust Gas Sensor Monitoring
a. Background
    Exhaust gas sensors (e.g., oxygen sensors, wide-range air-fuel (A/
F) sensors, NOX sensors) are important to the emission
control system of vehicles. These sensors are used for enhancing the
performance of several emission control technologies (e.g., catalysts,
EGR systems). We expect that both oxygen sensors and wide range A/F
sensors may be used by heavy-duty manufacturers to optimize their
emission control technologies. We would expect that, in addition to
their emissions control functions, these sensors will also be used to
satisfy many of the proposed HDOBD monitoring requirements, such as
fuel system monitoring, catalyst monitoring, and EGR system monitoring.
NOX sensors may also be used for optimization of several
diesel emission control technologies, such as NOX adsorbers
and selective catalytic reduction (SCR) systems. Since an exhaust gas
sensor can be a critical component of a vehicle's fuel and emission
control system, the proper performance of this component needs to be
assured to maintain low emissions. The reliance on these sensors for
emissions control and OBD monitoring makes it important that any
malfunction that adversely affects the performance of any of these
sensors be detected by the OBD system.
b. Exhaust Gas Sensor Monitoring Requirements
    We are proposing that the OBD system monitor all exhaust gas
sensors (e.g., oxygen, air-fuel ratio, NOX) used either for
emission control system feedback (e.g., EGR control/feedback, SCR
control/feedback, NOX adsorber control/feedback), or as a
monitoring device, for proper output signal, activity, response rate,
and any other parameter that can affect emissions. For engines equipped
with heated exhaust gas sensors, the OBD system would have to monitor
the heater for proper performance.
i. Air/Fuel Ratio Sensor Malfunctions
    For all air/fuel ratio sensors, we are proposing the following:
     Circuit malfunctions: The OBD system must detect
malfunctions of the sensor caused by either a lack of circuit
continuity or out-of-range values.
     Feedback malfunctions: The OBD system must detect a
malfunction of the sensor when a sensor failure or deterioration causes
an emissions control system--e.g., the EGR, SCR, or NOX
adsorber systems--to stop using that sensor as a feedback input (e.g.,
causes default or open-loop operation).
     Monitoring capability: To the extent feasible, the OBD
system must detect a malfunction of the sensor when the sensor output
voltage, resistance, impedance, current, amplitude, activity, offset,
or other characteristics are no longer sufficient for use as an OBD
system monitoring device (e.g., for catalyst, EGR, SCR, or
NOX adsorber monitoring).
    Specifically for sensors located upstream of an aftertreatment
device, we are proposing the following:
     Sensor performance malfunctions: The OBD system must
detect a malfunction prior to any failure or deterioration of the
sensor voltage, resistance, impedance, current, response rate,
amplitude, offset, or other characteristic(s) that would cause an
engine's emissions to exceed the applicable emissions thresholds for
``Other Monitors'' as shown in Table II.B-1.
    Specifically for sensors located downstream of an aftertreatment
device, we are proposing the following:
     Sensor performance malfunctions: The OBD system must
detect a malfunction prior to any failure or deterioration of the
sensor voltage, resistance, impedance, current, response rate,
amplitude, offset, or other characteristic(s) that would cause an
engine's emissions to exceed the applicable emissions thresholds for
``Air-fuel ratio sensors downstream of aftertreatment devices'' as
shown in Table II.B-1.
ii. NOX Sensor Malfunctions
    For NOX sensors, we are proposing the following:
     Sensor performance malfunctions: The OBD system must
detect a malfunction prior to any failure or deterioration of the
sensor voltage, resistance, impedance, current, response rate,
amplitude, offset, or other characteristic(s) that would cause an
engine's emissions to exceed the applicable emissions thresholds for
``NOX sensors'' as shown in Table II.B-1.
     Circuit malfunctions: The OBD system must detect
malfunctions of the sensor caused by either a lack of circuit
continuity or out-of-range values.
     Feedback malfunctions: The OBD system shall detect a
malfunction of the sensor when a sensor failure or deterioration causes
an emission control--e.g., the EGR, SCR, or NOX adsorber
systems--to stop using that sensor as a feedback input (e.g., causes
default or open-loop operation).
     Monitoring capability: To the extent feasible, the OBD
system must detect a malfunction of the sensor when the sensor output
voltage, resistance, impedance, current, amplitude, activity, offset,
or other characteristics are no longer sufficient for use as an OBD
system monitoring device (e.g., for catalyst, EGR, SCR, or
NOX adsorber monitoring).

iii. Other Exhaust Gas Sensor Malfunctions
    For other exhaust gas sensors, we are proposing that the
manufacturer submit a monitoring plan to the Administrator for
approval. The Administrator would approve the request upon determining
that the manufacturer has submitted data and an engineering evaluation
that demonstrate that the monitoring plan is as reliable and effective
as the monitoring plan required for air/fuel ratio sensors and
NOX sensors.
iv. Exhaust Gas Sensor Heater Malfunctions
    We are proposing that the OBD system detect a malfunction of the
heater performance when the current or voltage drop in the heater
circuit is no longer within the manufacturer's specified limits for
normal operation (i.e., within the criteria required to be met by the
component vendor for heater circuit performance at high mileage). The
manufacturer may use other malfunction criteria for heater performance
malfunctions. To do so, the manufacturer would be required to submit
data and/or engineering analyses that demonstrate that the monitoring
reliability and timeliness would be equivalent to the criteria stated
here. Further, the OBD system would be required to detect malfunctions
of the heater circuit including open or short circuits that conflict
with the commanded state of the heater (e.g., shorted to 12 Volts when
commanded to 0 Volts (ground)).
c. Exhaust Gas Sensor Monitoring Conditions
    For exhaust gas sensor performance malfunctions, we are proposing
that manufacturers define the monitoring conditions such that the
minimum performance ratio requirements discussed in section II.E would
be met. For purposes of tracking and reporting as required in section
II.E, all monitors used to detect sensor performance malfunctions would
have to be tracked separately but reported as a single set of values as
specified in section II.E.\32\
---------------------------------------------------------------------------

    \32\ For specific components or systems that have multiple
monitors that are required to be reported (e.g., exhaust gas sensor
bank 1 may have multiple monitors for sensor response or other
sensor characteristics), the OBD system must separately track
numerators and denominators for each of the specific monitors and
report only the corresponding numerator and denominator for the
specific monitor that has the lowest numerical ratio. If two or more
specific monitors have identical ratios, the corresponding numerator
and denominator for the specific monitor that has the highest
denominator shall be reported for the specific component.
---------------------------------------------------------------------------

    For exhaust gas sensor monitoring capability malfunctions,
manufacturers would have to define the monitoring conditions such that
the minimum performance ratio requirements discussed in section II.E
would be met with the exception that monitoring must occur every time
the monitoring conditions are met during the driving cycle rather than
once per driving cycle as required for most monitors.
    For exhaust gas sensor circuit malfunctions and feedback
malfunctions, monitoring must be conducted continuously.
    The manufacturer may disable continuous exhaust gas sensor
monitoring when an exhaust gas sensor malfunction cannot be
distinguished from other effects (e.g., disable ``out-of-range low''
monitoring during fuel cut conditions). To do so, the manufacturer
would be required to submit test data and/or engineering analyses that
demonstrate that a properly functioning sensor cannot be distinguished
from a malfunctioning sensor and that the disablement interval is
limited only to that necessary for avoiding a false detection.
    For exhaust gas sensor heater malfunctions, manufacturers must
define monitoring conditions such that the minimum performance ratio
requirements discussed in section II.E would be met. Monitoring for
sensor heater circuit malfunctions must be conducted continuously.
d. Exhaust Gas Sensor MIL Illumination and DTC Storage
    We are proposing the general requirements for MIL illumination and
DTC storage as discussed in section II.A.2.

C. Monitoring Requirements and Timelines for Gasoline/Spark-Ignition
Engines

    Table II.C-1 summarizes the proposed gasoline fueled spark ignition
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.C-
2 summarizes the proposed implementation schedule for these
thresholds--i.e., the proposed certification requirements and in-use
liabilities. More detail regarding the specific monitoring
requirements, implementation schedules, and liabilities can be found in
the sections that follow.

         Table II.C-1.--Proposed Emissions Thresholds for Gasoline Fueled SI Engines Over 14,000 Pounds
----------------------------------------------------------------------------------------------------------------
        Component/Monitor                  MY                 NMHC                 CO                 NOX
----------------------------------------------------------------------------------------------------------------
Catalytic converter system.......  2010+.............  1.75x.............  ..................  1.75x
``Other monitors'' with emissions  2010+.............  1.5x..............  1.5x..............  1.5x
 thresholds (see section II.C).
Evaporative emissions control      2010+.............  0.150 inch leak ..
 system.
----------------------------------------------------------------------------------------------------------------
Notes: MY=Model Year; 1.75x means a multiple of 1.75 times the applicable emissions standard; not all proposed
  monitors have emissions thresholds but instead rely on functionality and rationality checks as described in
  section II.D.4. The evaporative emissions control system threshold is not, technically, an emissions threshold
  but rather a leak size that must be detected; nonetheless, for ease we refer to this as the threshold.

    There are exceptions to the emissions thresholds shown in Table
II.C-1 whereby a manufacturer can demonstrate that emissions do not
exceed the threshold even when the component or system is non-
functional at which point a functional check would be allowed.
    The monitoring requirements described below for gasoline engines
mirror those that are already in place for gasoline engines used in
vehicles under 14,000 pounds. The HD gasoline industry--General Motors
and Ford, as of today \33\--have told us that their preference is to
use essentially the same OBD system on their engines used in both under
and over 14,000 pound vehicles.\34\ In general, we agree with the

HD gasoline industry on this issue for three reasons:
---------------------------------------------------------------------------

    \33\ This is true according to our certification database for
both he 2004 and 2005 model years. Other manufacturers certify
engines that use the Otto cycle, but those engines do not burn
gasoline and instead burn various alternative fuels.
    \34\ ``EMA Comments on Proposed HDOBD Requirements for HDGE,''
bullet items 3 and 4; April 28, 2005, Docket ID EPA-HQ-OAR-
2005-0047-0003.
---------------------------------------------------------------------------

     The engines used in vehicles above and below 14,000 pounds
are the same which makes it easy for industry to use the same OBD
monitors.
     The existing OBD requirements for engines used in vehicles
below 14,000 pounds have proven effective; and,
     The industry members have more than 10 years experience
complying with the OBD requirements for engines used in vehicles below
14,000 pounds.
    As a result, we are proposing requirements that should allow for
OBD system consistency in vehicles under and over 14,000 pounds rather
than proposing requirements that mirror the proposed HD diesel
requirements discussed in section II.B. Nonetheless, the requirements
proposed below are for engine-based OBD monitors only rather than
monitors for the entire powertrain (which would include the
transmission). We are doing this for the same reasons as done for the
proposed diesel OBD requirements in that certification of gasoline
applications over 14,000 pounds, like their diesel counterparts, is
done on an engine basis and not a vehicle basis.
1. Fuel System Monitoring
a. Background
    As with diesel engines, the fuel system of a gasoline engine is an
essential component of the engine's emissions control system. Proper
delivery of fuel is essential to maintain stoichiometric operation and
minimize engine out emissions. Proper stoichiometric control is also
critical to maximize catalyst conversion efficiency and reach low
tailpipe emission levels. As such, thorough monitoring of the fuel
system is an essential element in an OBD system.
    For gasoline engines, the fuel system generally includes a fuel
pump, fuel pressure regulator, fuel rail, individual injectors for each
cylinder, and a closed-loop feedback control system using oxygen
sensor(s) or air-fuel ratio (A/F) sensor(s). The feedback sensors are
located in the exhaust system and are used to regulate the fuel
injection quantity to achieve a stoichiometric mixture in the exhaust.
If the sensor indicates a rich (or lean) mixture, the system reduces
(or increases) the amount of fuel being injected by applying a short
term correction to the fuel injection quantity calculated for the
current engine operating condition. To account for aging or
deterioration in the system such as reduced injector flow, more
permanent long term corrections are also learned and applied to the
fuel injection quantity for more precise fueling.
    For gasoline engines, fuel system monitoring has been implemented
on light-duty vehicles since the 1996 model year and on heavy-duty
vehicles less than 14,000 pounds and the engines used in those vehicles
since the 2004/2005 model year. For heavy-duty gasoline engines used in
vehicles over 14,000 pounds (many of which are the same engine as is
used in vehicles less than 14,000 pounds), the system components and
control strategies are identical to those used in the light-duty and
under 14,000 pound categories. As such, the monitoring requirements
established for engines used in vehicles less than 14,000 pounds can be
directly applied to engines used in vehicles over 14,000 pounds.
b. Fuel System Monitoring Requirements
    We are proposing that the fuel system be continuously monitored for
its ability to maintain engine emissions below the applicable emissions
thresholds. Manufacturers would also be required to verify that the
fuel system is in closed-loop operation--e.g., that it is using the
oxygen sensor for feedback control. The individual components of the
fuel system would also be covered by separate monitoring requirements
for oxygen sensors, misfire (for the fuel injectors), and comprehensive
components (in systems such as those with electronically-controlled
variable speed fuel pumps or electronically-controlled fuel pressure
regulators).
i. Fuel System Performance
    We are proposing that the OBD system be required to detect a
malfunction of the fuel delivery system (including feedback control
based on a secondary oxygen sensor) when the fuel delivery system is
unable to maintain the engine's emissions at or below the applicable
emissions thresholds for ``Other monitors'' as shown in Table II.C-1.
ii. Fuel System Feedback Control
    If the engine is equipped with adaptive feedback control, we are
proposing that the OBD system be required to detect a malfunction when
the adaptive feedback control has used up all of the adjustment allowed
by the manufacturer. However, if the engine is equipped with feedback
control that is based on a secondary oxygen (or equivalent) sensor, the
OBD system would not be required to detect a malfunction of the fuel
system solely when the feedback control based on that secondary oxygen
sensor has used up all of the adjustment allowed by the manufacturer.
For such systems, the OBD system would be required to meet the fuel
system performance requirements presented above.
    Additionally, we are proposing that the OBD system be required to
detect a malfunction whenever the fuel control system fails to enter
closed loop operation within a time interval after engine startup. The
manufacturer would be required to submit data and/or engineering
analyses that support their chosen time interval.
    Lastly, manufacturers would be allowed to adjust the malfunction
criteria and/or monitoring conditions to compensate for changes in
altitude, temporary introduction of large amounts of purge vapor, or
for other similar identifiable operating conditions when they occur.
c. Fuel System Monitoring Conditions
    We are proposing that the OBD system monitor continuously for
malfunctions of the fuel system.
d. Fuel System MIL Illumination and DTC Storage
    We are proposing that a pending DTC be stored immediately upon
detecting a malfunction according to the fuel system monitoring
requirements presented in section II.C.1.b (i.e., rather than waiting
until the end of the drive cycle to store the pending DTC). Once a
pending DTC is stored, the OBD system would be required to illuminate
the MIL immediately and store a MIL-on DTC if a malfunction is again
detected during either of the following two events: (1) The drive cycle
immediately following the drive cycle during which the pending DTC was
stored, regardless of the conditions encountered during the drive
cycle; or, (2) on the next drive cycle during which similar conditions
are encountered to those that occurred when the pending DTC was
stored.\35\
---------------------------------------------------------------------------

    \35\ ``Similar conditions,'' as used in conjunction with misfire
and fuel system monitoring, means engine conditions having an engine
speed within 375 rpm, load conditions within 20 percent, and the
same warm up status (i.e., cold or hot) as existing during the
applicable previous problem detection. The Administrator may approve
other definitions of similar conditions based on comparable
timeliness and reliability in detecting similar engine operation.
---------------------------------------------------------------------------

    We are also proposing that the pending DTC may be erased at the end
of the next drive cycle in which similar conditions have been
encountered without detecting a malfunction according to the fuel
system monitoring requirements. The pending DTC may also be erased if
similar conditions are not encountered during the 80 drive cycles
immediately after the initial

detection of a malfunction for which the pending DTC was set.
    We are proposing some specific requirements with respect to storage
of freeze frame information associated with fuel system malfunctions.
First, the OBD system must store and erase freeze frame information
either in conjunction with storing and erasing a pending DTC or in
conjunction with storing and erasing a MIL-on DTC. Second, if freeze
frame information is already stored for a malfunction other than an
engine misfire or fuel system malfunction at the time that a fuel
system DTC is stored, the preexisting freeze frame information must be
replaced with freeze frame information regarding the fuel system
malfunction.
    The OBD system would also be required to store the engine speed,
load, and warm up status present when the first fuel system malfunction
is detected that resulted in the storage of the pending DTC. The MIL
may be extinguished after three sequential drive cycles in which
similar conditions have been encountered without detecting a
malfunction of the fuel system.
2. Engine Misfire Monitoring
a. Background
    Detecting engine misfire on a gasoline spark ignition engine is
important for two reasons: Its impact on the emissions performance of
the engine and its impact on the durability of the catalytic converter.
Engine misfire has two primary causes: Lack of spark and poor fuel
metering (delivery). When misfire occurs, unburned fuel and air are
pumped out of the engine and into the exhaust system and into the
catalyst. This can increase dramatically the operating temperature of
the catalyst where temperatures can soar to above 900 degrees Celsius.
This problem is usually most severe under high load/high speed engine
operating conditions and can cause irreversible damage to the catalyst.
Though the durability of catalysts has been improving, most are unable
to sustain continuous operation at such high temperatures. Engine
misfire also contributes to poor emissions performance, especially when
the misfire occurs during engine warm-up and the catalyst itself has
not yet reached its operating temperature.
b. Engine Misfire Monitoring Requirements
    We are proposing that the OBD system detect both engine misfire
capable of causing catalyst damage and engine misfire capable of
causing poor emissions performance. Additionally, the OBD system would
be required to identify the specific cylinder in which misfire is
occurring and/or if there exists a condition in which more than one
cylinder is misfiring; when identifying a multiple cylinder misfire
condition, the OBD system would not be required to identify
individually each of the misfiring cylinders. We are proposing an
exception to this whereby if more than 90 percent of the detected
misfires are occurring in a single cylinder, the manufacturer may elect
to consider it a single cylinder misfire condition rather than a
multiple cylinder misfire condition. However, we are proposing that, if
two or more cylinders individually have more than 10 percent of the
total number of detected misfires, the manufacturer must consider it a
multiple cylinder misfire condition.
i. Engine Misfire Capable of Causing Catalyst Damage
    We are proposing that the manufacturer be required to detect the
percentage of misfire--evaluated in 200 revolution increments--for each
engine speed and load condition that would result in a temperature
capable of damaging the catalyst. For every engine speed and load
condition at which this percentage is determined to be less than five
percent, the manufacturer may set the malfunction criteria at five
percent. The manufacturer may use a longer interval than a 200
revolution increment but only for determining, on a given drive cycle,
the first misfire exceedance; upon detecting the first such exceedance,
the 200 revolution increment must be used. The manufacturer may use a
longer initial interval by submitting data and/or engineering analyses
that demonstrate that catalyst damage would not occur due to
unacceptably high catalyst temperatures before the interval has
elapsed.
    Further, we are proposing that, for the purpose of establishing the
temperature at which catalyst damage would occur, manufacturers not be
allowed to define the catalyst damaging temperature at a temperature
more severe than what the catalyst system could be operated at for 10
consecutive hours and still meet the applicable standards.
ii. Engine Misfire Causing Poor Emissions Performance
    We are proposing that the manufacturer be required to detect the
percentage of misfire--evaluated in 1000 revolution increments--that
would cause emissions to exceed the emissions thresholds for ``Other
monitors'' as shown in Table II.C-1 if that percentage of misfire were
present from the beginning of the test procedure. To establish this
percentage of misfire, the manufacturer would be required to use
misfire events occurring at equally spaced, complete engine cycle
intervals, across randomly selected cylinders throughout each 1000
revolution increment. If this percentage of misfire is determined to be
lower than one percent, the manufacturer may set the malfunction
criteria at one percent. The manufacturer may use a different interval
than a 1000 revolution increment. To do so, the manufacturer would be
required to submit data and/or engineering analyses demonstrating that
the strategy would be equally effective and timely at detecting
misfire. A malfunction must be detected if the percentage of misfire is
exceeded regardless of the pattern of misfire events (e.g., random,
equally spaced, continuous).
c. Engine Misfire Monitoring Conditions
    We are proposing that the OBD system monitor continuously to detect
engine misfire under all of the following conditions:
     From no later than the end of the second crankshaft
revolution after engine start;
     During the rise time and settling time as the engine
reaches the desired idle speed immediately following engine start-up
(i.e., ``flare-up'' and ``flare-down''); and,
     Under all positive torque conditions except within the
engine operating region bound by lines connecting the following three
points: An engine speed of 3000 rpm with the engine load at the
positive torque line (i.e., engine load with the transmission in
neutral), an engine speed at the redline rpm with the engine load at
the positive torque line, and an engine speed at the redline rpm with
an engine load at which intake manifold vacuum is four inches of
mercury lower than that at the positive torque line (this would be an
engine load somewhat greater than the engine load at the positive
torque line).\36\
---------------------------------------------------------------------------

    \36\ ``Redline engine speed'' is actually defined by the
manufacturer as either the recommended maximum engine speed as
normally displayed on instrument panel tachometers or the engine
speed at which fuel shutoff occurs.
---------------------------------------------------------------------------

    If a monitoring system cannot detect all misfire patterns under the
required engine speed and load conditions, the manufacturer may request
approval of the system nonetheless. In evaluating the manufacturer's
request, the Administrator would consider:
     The magnitude of the region(s) in which misfire detection
is limited;
     The degree to which misfire detection is limited in those
region(s)

(i.e., the probability of detection of misfire events);
     The frequency with which said region(s) are expected to be
encountered in-use;
     The type of misfire patterns for which misfire detection
is troublesome; and,
     Demonstration that the monitoring technology being used is
not inherently incapable of detecting misfire under the required
conditions (i.e., compliance can be achieved by other manufacturers on
their engines).
    The Administrator's evaluation would be based on the following
misfire patterns:
     Equally spaced misfire occurring on randomly selected
cylinders;
     Single cylinder continuous misfire; and,
     Paired cylinder (cylinders firing at the same crank angle)
continuous misfire.
    Further, a manufacturer may use a monitoring system that has
reduced misfire detection capability during the portion of the first
1000 revolutions after engine start during which a cold start emission
reduction strategy is active that reduces engine torque (e.g., spark
retard strategies). To do so, the manufacturer would be required to
submit data and/or engineering analyses demonstrating that the
probability of detection is greater than or equal to 75 percent during
the worst case condition (i.e., lowest generated torque) for a vehicle
operated continuously at idle (park/neutral idle) on a cold start
between 50 and 86 degrees Fahrenheit and that the technology cannot
reliably detect a higher percentage of the misfire events during these
conditions.
    A manufacturer may disable misfire monitoring or use an alternative
malfunction criterion when misfire cannot be distinguished from other
effects. To do so, the manufacturer would be required to submit data
and/or engineering analyses demonstrating that the disablement interval
or period of use of an alternative malfunction criterion is limited
only to that necessary for avoiding a false detection (errors of
commission). Such disablements would be allowed for conditions
involving:
     Rough road;
     Fuel cut;
     Gear changes for manual transmission vehicles;
     Traction control or other vehicle stability control
activation such as anti-lock braking or other engine torque
modifications to enhance vehicle stability;
     Off-board control or intrusive activation of vehicle
components or diagnostics during service or assembly plant testing;
     Portions of intrusive evaporative system or EGR
diagnostics that can significantly affect engine stability (i.e., while
the purge valve is open during the vacuum pull-down of a evaporative
system leak check but not while the purge valve is closed and the
evaporative system is sealed or while an EGR diagnostic causes the EGR
valve to be intrusively cycled on and off during positive torque
conditions); or,
     Engine speed, load, or torque transients due to throttle
movements more rapid than occurs over the FTP cycle for the worst case
engine within each engine family.
    Additionally, the manufacturer may disable misfire monitoring when
the fuel level is 15 percent or less of the nominal capacity of the
fuel tank, when PTO units are active, or while engine coolant
temperature is below 20 degrees Fahrenheit. For the latter case, the
manufacturer may continue the misfire monitoring disablement until
engine coolant temperature exceeds 70 degrees Fahrenheit provided the
manufacturer can demonstrate that it is necessary.
    In general, the Administrator would not approve misfire monitoring
disablement for conditions involving normal air conditioning compressor
cycling from on-to-off or off-to-on, automatic transmission gear shifts
(except for shifts occurring during wide open throttle operation),
transitions from idle to off-idle, normal engine speed or load changes
that occur during the engine speed rise time and settling time (i.e.,
``flare-up'' and ``flare-down'') immediately after engine starting
without any vehicle operator-induced actions (e.g., throttle stabs), or
excess acceleration (except for acceleration rates that exceed the
maximum acceleration rate obtainable at wide open throttle while the
vehicle is in gear due to abnormal conditions such as slipping of a
clutch).
    Further, the manufacturer may request approval of other misfire
monitoring disablements or use of alternative malfunction criteria for
any other condition. The Administrator would consider such requests on
a case by case basis and will consider whether or not the manufacturer
has demonstrated that the request is based on an unusual or unforeseen
circumstance and that it is applying the best available computer and
monitoring technology.
    For engines with more than eight cylinders that cannot meet the
continuous monitoring and detection requirements listed above, a
manufacturer may use alternative misfire monitoring conditions. Any
manufacturer wishing to use alternative misfire monitoring conditions
must submit data and/or an engineering evaluation that demonstrate that
misfire detection throughout the required operating region cannot be
achieved when using proven monitoring technology (i.e., a technology
that provides for compliance with these requirements on other engines)
and provided misfire is detected to the fullest extent permitted by the
technology. However, the misfire detection system would still be
required to monitor during all positive torque operating conditions
encountered during an FTP transient cycle.
d. Engine Misfire MIL Illumination and DTC Storage
    Manufacturers may store a general misfire DTC instead of a cylinder
specific DTC under certain operating conditions. Do so shall depend on
the manufacturer submitting data and/or an engineering evaluation that
demonstrate that the specific misfiring cylinder cannot be reliably
identified when the certain operating conditions occur.
i. Engine Misfire Capable of Causing Catalyst Damage
    We are proposing that a pending DTC shall be stored immediately if,
during a single drive cycle, the percentage of misfire determined by
the manufacturer as being capable of causing catalyst damage is
exceeded three times when operating in the positive torque region
encountered during an FTP transient cycle or is exceeded on a single
occasion when operating at any other engine speed and load condition in
the positive torque region defined above. Immediately after a pending
DTC is stored, the MIL shall blink once per second at all times while
misfire is occurring during the drive cycle (i.e., the MIL may be
extinguished during those times when misfire is not occurring during
the drive cycle). If, at the time such a catalyst damaging engine
misfire is occurring, the MIL is already illuminated for a malfunction
other than engine misfire, the MIL shall blink similarly while the
engine misfire is occurring and, if the misfire ceases, the MIL shall
stop blinking but shall remain illuminated as commanded by the other
malfunction.
    If a pending DTC is stored as described above, the OBD system shall
immediately store a MIL-on DTC if the percentage of misfire determined
by the manufacturer as being capable of causing catalyst damage is
again exceeded one or more times during either: (a) the drive cycle
immediately

following the storage of the pending DTC, regardless of the conditions
encountered during the drive cycle; or, (b) on the next drive cycle in
which similar conditions are encountered to those that existed when the
pending DTC was stored.
    If, during a previous drive cycle, a pending DTC has been stored
associated with detection of an engine misfire capable of causing poor
emissions performance, the OBD system shall immediately store a MIL-on
DTC if the percentage of misfire determined by the manufacturer as
capable of causing catalyst damage is exceeded, regardless of the
conditions encountered.
    Upon storage of a MIL-on DTC associated with engine misfire capable
of causing catalyst damage, the MIL shall blink as described above
while the engine misfire is occurring and then shall remain
continuously illuminated if the engine misfire ceases. This MIL
illumination logic shall continue until the requirements for
extinguishing the MIL are met, as described below.
    If the engine misfire is not again detected by the end of the next
drive cycle in which similar conditions are encountered to those that
existed when the pending DTC was stored then the pending DTC shall be
erased. The pending DTC may also be erased if similar conditions are
not encountered during the 80 drive cycles subsequent to the initial
malfunction detection.
    We are also proposing that engines with fuel shutoff and default
fuel control--that are used to prevent catalyst damage should engine
misfire capable of causing catalyst damage be detected--shall have some
exemptions from these MIL illumination requirements. Most notably, the
MIL is not required to blink while the catalyst damaging misfire is
occurring. Instead, the MIL may simply illuminate in a steady fashion
while the misfire is occurring provided that the fuel shutoff and
default fuel control are activated as soon as the misfire is detected.
Fuel shutoff and default fuel control may be deactivated only to permit
fueling outside of the misfire range. Manufacturers may also
periodically, but not more than once every 30 seconds, deactivate fuel
shutoff and default fuel control to determine if the catalyst damaging
misfire is still occurring. Normal fueling and fuel control may be
resumed if the catalyst damaging misfire is no longer being detected.
    Manufacturers may also use a MIL illumination strategy that
continuously illuminates the MIL in lieu of blinking the MIL during
extreme misfire conditions capable of causing catalyst damage (i.e.,
misfire capable of causing catalyst damage that is occurring at all
engine speeds and loads). Manufacturers would be allowed to use such a
strategy only when catalyst damaging misfire levels cannot be avoided
during reasonable driving conditions and the manufacturer can
demonstrate that the strategy will encourage operation of the vehicle
in conditions that will minimize catalyst damage (e.g., at low engine
speeds and loads).
ii. Engine Misfire Causing Poor Emissions Performance
    We are proposing that, for a misfire detected within the first 1000
revolutions after engine start during which misfire detection is
active, a pending DTC shall be stored after the first exceedance of the
percentage of misfire determined by the manufacturer as capable of
causing poor emissions performance. If a pending DTC is stored, the OBD
system shall illuminate the MIL and store a MIL-on DTC within 10
seconds if an exceedance of the percentage of misfire is again detected
in the first 1000 revolutions during any subsequent drive cycle,
regardless of the conditions encountered during the driving cycle. The
pending DTC shall be erased at the end of the next drive cycle in which
similar conditions are encountered to those that existed when the
pending DTC was stored provided the specified percentage of misfire is
not again detected. The pending DTC may also be erased if similar
conditions are not encountered during the 80 drive cycles subsequent to
the initial malfunction detection.
    For a misfire detected after the first 1000 revolutions following
engine start, a pending DTC shall be stored no later than after the
fourth exceedance--during a single drive cycle--of the percentage of
misfire determined by the manufacturer as being capable of causing poor
emissions performance. If a pending DTC is stored, the OBD system shall
illuminate the MIL and store a MIL-on DTC within 10 seconds if an
exceedance of the percentage of misfire is again detected four times
during: (a) the drive cycle immediately following the storage of the
pending DTC, regardless of the conditions encountered during the drive
cycle; or, (b) on the next drive cycle in which similar conditions are
encountered to those that existed when the pending DTC was stored. The
pending DTC shall be erased at the end of the next drive cycle in which
similar conditions are encountered to those that existed when the
pending DTC was stored provided the specified percentage of misfire is
not again detected. The pending DTC may also be erased if similar
conditions are not encountered during the 80 drive cycles subsequent to
the initial malfunction detection.
    We are proposing some specific items with respect to freeze frame
storage associated with engine misfire. The OBD system shall store and
erase freeze frame conditions either in conjunction with storing and
erasing a pending DTC or in conjunction with storing a MIL-on DTC and
erasing a MIL-on DTC. In addition to those proposed requirements
discussed in section II.A.2, we are proposing that, if freeze frame
conditions are stored for a malfunction other than a misfire
malfunction when a DTC is stored, the previously stored freeze frame
information shall be replaced with freeze frame information regarding
the misfire malfunction (i.e., the misfire's freeze frame information
should take precedence over freeze frames for other malfunctions).
Further, we are proposing that, upon detection of misfire, the OBD
system store the following engine conditions: engine speed, load, and
warm up status of the first misfire event that resulted in the storage
of the pending DTC.
    Lastly, we are proposing that the MIL may be extinguished after
three sequential driving cycles in which similar conditions have been
encountered without an exceedance of the specified percentage of
misfire.
3. Exhaust Gas Recirculation (EGR) Monitoring
a. Background
    EGR works to reduce NOX emissions the same way in
gasoline engines as described earlier for diesel engines. First, the
recirculated exhaust gases dilute the intake air--i.e., oxygen in the
fresh air is displaced with relatively non-reactive exhaust gases--
which, in turn, results in less oxygen to form NOX. Second,
EGR absorbs heat from the combustion process which reduces combustion
chamber temperatures which, in turn, reduces NOX formation.
The amount of heat absorbed from the combustion process is a function
of EGR flow rate and recirculated gas temperature, both of which are
controlled to minimize NOX emissions. EGR systems can
involve many components to ensure accurate control of EGR flow,
including valves, valve position sensors, and actuators.
b. EGR System Monitoring Requirements
    We are proposing that the OBD system monitor the EGR system on
engines so equipped for low and high

flow rate malfunctions. The individual electronic components (e.g.,
actuators, valves, sensors) that are used in the EGR system must be
monitored in accordance with the comprehensive component requirements
in section II.D.4.
i. EGR Low Flow Malfunctions
    We are proposing that the OBD system detect a malfunction prior to
a decrease from the manufacturer's specified EGR flow rate that would
cause an engine's emissions to exceed the emissions thresholds for
``other monitors'' as shown in Table II.C-1. For engines in which no
failure or deterioration of the EGR system that causes a decrease in
flow could result in an engine's emissions exceeding the applicable
emissions thresholds, the OBD system would have to detect a malfunction
when the system has reached its control limits such that it cannot
increase EGR flow to achieve the commanded flow rate.
ii. EGR High Flow Malfunctions
    We are proposing that the OBD system detect a malfunction of the
EGR system, including a leaking EGR valve--i.e., exhaust gas flowing
through the valve when the valve is commanded closed--prior to an
increase from the manufacturer's specified EGR flow rate that would
cause an engine's emissions to exceed the emissions thresholds for
``other monitors'' as shown in Table II.C-1. For engines in which no
failure or deterioration of the EGR system that causes an increase in
flow could result in an engine's emissions exceeding the applicable
emissions thresholds, the OBD system would have to detect a malfunction
when the system has reached its control limits such that it cannot
reduce EGR flow to achieve the commanded flow rate.
c. EGR System Monitoring Conditions
    We are proposing that manufacturers define the monitoring
conditions for EGR system malfunctions such that the minimum
performance ratio requirements discussed in section II.E would be met.
For purposes of tracking and reporting as required in section II.E, all
monitors used to detect EGR low flow and high flow malfunctions must be
tracked separately but reported as a single set of values as specified
in section II.E.\37\
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    \37\ For specific components or systems that have multiple
monitors that are required to be reported (e.g., exhaust gas sensor
bank 1 may have multiple monitors for sensor response or other
sensor characteristics), the OBD system must separately track
numerators and denominators for each of the specific monitors and
report only the corresponding numerator and denominator for the
specific monitor that has the lowest numerical ratio. If two or more
specific monitors have identical ratios, the corresponding numerator
and denominator for the specific monitor that has the highest
denominator shall be reported for the specific component.
---------------------------------------------------------------------------

    Manufacturers may temporarily disable the EGR system monitor under
conditions when monitoring may not be reliable (e.g., when freezing may
affect performance of the system). Such temporary disablement would be
allowed provided the manufacturer has submitted data and/or an
engineering evaluation that demonstrate that the EGR monitor cannot be
done reliably when these specific conditions exist.
d. EGR System MIL Illumination and DTC Storage
    We are proposing the general requirements for MIL illumination and
DTC storage as discussed in section II.A.2.
4. Cold Start Emission Reduction Strategy Monitoring
a. Background
    The largest portion of exhaust emissions from gasoline engines is
generated during the brief period following startup before the engine
and catalyst have warmed up to their normal operating temperatures. To
meet increasingly stringent emissions standards, manufacturers are
developing hardware and associated control strategies to reduce these
``cold start'' emissions. Most efforts center on reducing catalyst
warm-up time.
    A cold catalyst is heated mainly by two mechanisms: heat
transferred from the exhaust gases to the catalyst; and, heat generated
in the catalyst as a result of the exothermic catalytic reactions. Most
manufacturers use substantial spark retard and/or increased idle speed
following a cold engine start, both of which maximize the heat
available in the exhaust gases which, in turn, increases the heat
transfer to the catalyst. Vehicle drivability and engine idle quality
concerns tend to limit the amount of spark retard and/or increased idle
speed that a manufacturer can use to accelerate catalyst warm up. These
strategies or, more correctly, the systems used to employ these
strategies--the ignition system for spark retard and the idle control
system for control of engine speed--are normally monitored only after
engine warm-up. Therefore, any malfunctions that might occur during the
cold start event may not be detected by the OBD system. This could have
significant emissions consequences due to the unknown loss of emissions
control during the time following engine startup.
    This concern is exacerbated by the high cost of precious metals--
the platinum group metals (PGM) platinum, palladium, and rhodium--which
motivates industry to minimize their use in catalysts. To compensate
for the resultant reduction in overall catalyst performance,
manufacturers will likely use increasingly more aggressive cold start
emission reduction strategies in an attempt to further reduce cold
start emissions. These strategies must be successful--and be properly
monitored--to meet the more stringent 2008 emissions standards and to
maintain low emissions in-use.
b. Cold Start Emission Reduction Strategy Monitoring Requirements
    We are proposing that, if an engine incorporates an engine control
strategy specifically to reduce cold start emissions, the OBD system
must monitor the key components (e.g., idle air control valve), other
than the secondary air system, while the control strategy is active to
ensure that the control strategy is operating properly. Secondary air
systems would have to be monitored separately as discussed in section
II.C.5.
    The OBD system would be required to detect a malfunction prior to
any failure or deterioration of the individual components associated
with the cold start emissions reduction control strategy that would
cause an engine's emissions to exceed the emissions thresholds for
``other monitors'' as shown in Table II.C-1. For components where no
failure or deterioration of the component used by the cold start
emission reduction strategy could result in an engine's emissions
exceeding the applicable emissions thresholds, the individual
components would have to be monitored for proper functional response as
described in section II.D.4 while the control strategy is active.
    Manufacturers would be required to establish the appropriate
malfunction criteria based on data from one or more representative
engine(s). Further, manufacturers would be required to provide an
engineering evaluation for establishing the malfunction criteria for
the remainder of the manufacturer's product line. An annual evaluation
of these criteria by the Administrator may not be necessary provided
the manufacturer can demonstrate that any technological changes from
one year to the next do not affect the previously approved malfunction
criteria.
c. Cold Start Emission Reduction Strategy Monitoring Conditions
    We are proposing that manufacturers define the monitoring
conditions for

malfunctions of the cold start emissions reduction strategy such that
the minimum performance ratio requirements discussed in section II.E
would be met.
d. Cold Start Emission Reduction Strategy MIL Illumination and DTC
Storage
    We are proposing the general requirements for MIL illumination and
DTC storage as discussed in section II.A.2.
5. Secondary Air System Monitoring
a. Background
    Secondary air systems--expected to be used on gasoline engines
only--are used to reduce cold start emissions of hydrocarbons and
carbon monoxide. Many of today's engines operate near stoichiometry
after a cold engine start. However, the future more stringent emission
standards may require the addition of a secondary air system in
combination with a richer than stoichiometric cold start mixture. Such
an approach could quickly warm up the catalyst for improved cold start
emissions performance.
    Secondary air systems typically consist of an electric air pump,
various hoses, and check valves to deliver outside air to the exhaust
system upstream of the catalytic converter(s). This system usually
operates only after a cold engine start and usually for only a brief
period of time. When the electric air pump is operating, fresh air is
delivered into the exhaust where it mixes with and ignites any unburned
fuel. This serves to warm up the catalyst far more rapidly than would
otherwise occur. Any problems that might occur in the field--corroded
check valves, damaged tubing and hoses, malfunctioning air switching
valves--could cause cold start emissions performance to suffer.
Therefore, monitoring is needed given the importance of a properly
functioning secondary air system to emissions performance.
b. Secondary Air System Monitoring Requirements
    We are proposing that the OBD system on engines equipped with any
form of secondary air delivery system be required to monitor the proper
functioning of the secondary air delivery system, including all air
switching valve(s). The individual electronic components (e.g.,
actuators, valves, sensors) in the secondary air system would have to
be monitored in accordance with the comprehensive component
requirements discussed in section II.D.4.
i. Secondary Air System Low Flow Malfunctions
    We are proposing that the OBD system detect a secondary air system
malfunction prior to a decrease from the manufacturer's specified air
flow during normal operation that would cause an engine's emissions to
exceed the emissions thresholds for ``other monitors'' as shown in
Table II.C-1.\38\ For engines in which no deterioration or failure of
the secondary air system would result in an engine's emissions
exceeding any of the applicable emissions thresholds, the OBD system
would have to detect a malfunction when no detectable amount of air
flow is delivered during normal operation of the secondary air system.
---------------------------------------------------------------------------

    \38\ For purposes of secondary air system malfunctions, ``air
flow'' is defined as the air flow delivered by the secondary air
system to the exhaust system. For engines using secondary air
systems with multiple air flow paths/distribution points, the air
flow to each bank (i.e., a group of cylinders that share a common
exhaust manifold, catalyst, and control sensor) must be monitored in
accordance with these malfunction criteria. Also, ``normal
operation'' is defined as the condition where the secondary air
system is activated during catalyst and/or engine warm-up following
engine start. ``Normal operation'' does not include the condition
where the secondary air system is intrusively turned on solely for
the purpose of monitoring.
---------------------------------------------------------------------------

ii. Secondary Air System High Flow Malfunctions
    We are proposing that the OBD system detect a secondary air system
malfunction prior to an increase from the manufacturer's specified air
flow during normal operation that would cause an engine's emissions to
exceed the emissions thresholds for ``other monitors'' as shown in
Table II.C-1.\39\ For engines in which no deterioration or failure of
the secondary air system would result in an engine's emissions
exceeding any of the applicable emissions thresholds, the OBD system
would have to detect a malfunction when no detectable amount of air
flow is delivered during normal operation of the secondary air system.
---------------------------------------------------------------------------

    \39\ Ibid.
---------------------------------------------------------------------------

c. Secondary Air System Monitoring Conditions
    We are proposing that manufacturers define the monitoring
conditions for malfunctions of the secondary air system such that the
minimum performance ratio requirements discussed in section II.E would
be met. For purposes of tracking and reporting as required in section
II.E, all monitors used to detect malfunctions of the secondary air
system during its normal operation must be tracked separately but
reported as a single set of values as specified in section II.E
d. Secondary Air System MIL Illumination and DTC Storage
    We are proposing the general requirements for MIL illumination and
DTC storage as discussed in section II.A.2.
6. Catalytic Converter Monitoring
a. Background
    Three-way catalysts are one of the most important emission-control
components on gasoline engines. They consist of ceramic or metal
substrates coated with the one or more of the platinum group metals
(PGM) platinum, palladium, and rhodium. These PGMs are dispersed within
an alumina washcoat containing ceria, and the substrates are mounted in
a stainless steel container in the vehicle exhaust system. Three-way
catalysts are capable of oxidizing HC emissions, oxidizing CO
emissions, and reducing NOX emissions, hence the term three-
way.
    While continuous improvements to catalysts have increased their
durability, their performance still deteriorates, especially when
subjected to very high temperatures. Such high temperatures can be
caused by, among other factors, engine misfire which results in
unburned fuel and air entering and igniting in the catalyst. Exposure
to such high temperatures will result in reduced catalyst conversion
efficiency. Catalyst efficiency can also deteriorate via poisoning if
exposed to lead, phosphorus, or high sulfur levels. Catalysts can also
fail by mechanical means such as excessive vibration. Given its
importance to emissions control and the many factors that can reduce
its effectiveness, the catalyst is one of the most important components
to be monitored.
b. Catalytic Converter Monitoring Requirements
    We are proposing that the OBD system monitor the catalyst system
for proper conversion capability. Specifically, the OBD system would be
required to detect a catalyst system malfunction when the catalyst
system's conversion capability decreases to the point that any of the
following occurs:
     NMHC and/or NOX emissions exceed the emissions
thresholds for the ``catalytic converter system'' as shown in Table
II.C-1.
    For purposes of determining the catalyst system malfunction
criteria the manufacturer would be required to use a catalyst system
deteriorated to the malfunction criteria using methods established by
the manufacturer to

represent real world catalyst deterioration under normal and
malfunctioning operating conditions. The malfunction criteria must be
established by using a catalyst system with all monitored and
unmonitored catalysts simultaneously deteriorated to the malfunction
criteria.\40\ For engines using fuel shutoff to prevent over-fueling
during misfire conditions (see section II.C.2), the malfunction
criteria could be established using a catalyst system with all
monitored catalysts simultaneously deteriorated to the malfunction
criteria and all unmonitored catalysts deteriorated to the end of the
engine's useful life.
---------------------------------------------------------------------------

    \40\ The unmonitored portion of the catalyst system would be
that portion downstream of the sensor(s) used for catalyst
monitoring.
---------------------------------------------------------------------------

c. Catalytic Converter Monitoring Conditions
    We are proposing that manufacturers define the monitoring
conditions for malfunctions of the catalytic converter system such that
the minimum performance ratio requirements discussed in section II.E
would be met. For purposes of tracking and reporting as required in
section II.E, all monitors used to detect malfunctions of the catalytic
converter system during its normal operation must be tracked separately
but reported as a single set of values as specified in section II.E.
d. Catalytic Converter MIL Illumination and DTC Storage
    We are proposing the general requirements for MIL illumination and
DTC storage as discussed in section II.A.2. Note that the monitoring
method for the catalyst(s) would have to be capable of detecting all
instances, except diagnostic self-clearing, when a catalyst DTC has
been cleared but the catalyst has not been replaced (e.g., catalyst
over temperature histogram approaches are not acceptable).
7. Evaporative Emission Control System Monitoring
a. Background
    The evaporative emission control system controls HC emissions that
would otherwise evaporate from the vehicle's fuel tank and fuel lines.
Should any leak develop in the evaporative emission control system--
e.g., a disconnected hose--the HC emissions can be quite high and well
over the evaporative emissions standards. Additionally, evaporative
purge system defects--e.g., deteriorated vacuum lines, damaged
canisters, non-functioning purge control valves--may occur which could
also result in very high evaporative emissions.
b. Evaporative System Monitoring Requirements
    We are proposing that the OBD system verify purge flow from the
evaporative system and detect any vapor leaks from the complete
evaporative system, excluding the tubing and connections between the
purge valve and the intake manifold. Individual components of the
evaporative system (e.g. valves, sensors) must be monitored in
accordance with the comprehensive components requirements discussed in
section II.D.4.
    The OBD system would be required to detect an evaporative system
malfunction when any of the following conditions exist:
     No purge flow from the evaporative system to the engine
can be detected by the OBD system (i.e., the ``purge flow''
requirement); or
     For the 2010 and later model years, the complete
evaporative system contains a leak or leaks that cumulatively are
greater than or equal to a leak caused by a 0.150 inch diameter orifice
(i.e., the ``system leak'' requirement).\41\
---------------------------------------------------------------------------

    \41\ In their HDOBD regulation, 13 CCR 1971.1, CARB defines
``orifice'' as an O'Keefe Controls Co. precision metal ``Type B''
orifice with NPT connections with a diameter of the specified
dimension (e.g., part number B-31-SS for a stainless steel 0.031
inch diameter orifice).
---------------------------------------------------------------------------

    If the most reliable monitoring method available cannot reliably
detect a system leak as specified above, a manufacturer may design
their system to detect a larger leak. The manufacturer would be
required to provide data and/or engineering analyses that demonstrate
the inability of the monitor to reliably detect the required leak and
their justification for detecting at their proposed orifice size.
Further, if the manufacturer can demonstrate that leaks of the required
size cannot cause evaporative or running loss emissions to exceed 1.5
times the applicable evaporative emissions standards, the Administrator
would revise upward the required leak size to the size demonstrated by
the manufacturer that would result in emissions exceeding 1.5 times the
standards.
c. Evaporative System Monitoring Conditions
    We are proposing that manufacturers define the monitoring
conditions for both purge flow and system leak malfunctions such that
the minimum performance ratio requirements discussed in section II.E
would be met. For purposes of tracking and reporting as required in
section II.E, all monitors used to detect system leak malfunctions must
be tracked separately but reported as a single set of values as
specified in section II.E.
    Manufacturers may disable or abort an evaporative emission control
system monitor when the fuel tank level is over 85 percent of nominal
tank capacity or during a refueling event. Manufacturers may design
their evaporative emission control system monitor such that it executes
only during drive cycles determined by the manufacturer to be cold
starts if such a condition is needed to ensure reliable monitoring. The
manufacturer would have to provide data and/or an engineering
evaluation demonstrating that a reliable check can only be made on
drive cycles when the cold start criteria are satisfied. However, the
manufacturer may not determine a cold start solely on the basis that
ambient temperature is higher than engine coolant temperature at engine
start. Lastly, manufacturers would be allowed to disable temporarily
the evaporative purge system to perform an evaporative system leak
check.
d. Evaporative System MIL Illumination and DTC Storage
    We are proposing the general requirements for MIL illumination and
DTC storage as discussed in section II.A.2, with an exception for leaks
associated with the fuel filler cap. If the OBD system is capable of
discerning that a system leak is being caused by a missing or
improperly secured fuel filler cap, the manufacturer is not required to
illuminate the MIL or store a DTC provided the vehicle is equipped with
an alternative indicator for notifying the vehicle operator of the fuel
filler cap ``malfunction.'' The alternative indicator would have to be
of sufficient illumination and location to be readily visible to the
vehicle operator under all lighting conditions. However, if the vehicle
is not equipped with an alternative indicator and, instead, the MIL is
illuminated to inform the operator of the ``malfunction,'' the MIL may
be extinguished and the corresponding DTC(s) erased once the OBD system
has verified that the fuel filler cap has been securely fastened and
the MIL has not been commanded ON for any other type of malfunction.
The Administrator may approve other strategies provided the
manufacturer was able to demonstrate that the vehicle operator would be
promptly notified of the missing or improperly secured fuel filler cap
and that the notification would reasonably result in corrective action
being undertaken.

8. Exhaust Gas Sensor Monitoring
a. Background
    Exhaust gas sensors (e.g., oxygen sensors, air-fuel ratio (A/F)
sensors) are a critical element of the emissions control system on
gasoline engines. In addition to maintaining a stoichiometric air-fuel
mixture and, thus, helping to achieve the lowest possible emissions,
these sensors are also used for enhancing the performance of several
emission control technologies--e.g., catalysts, EGR systems). Many
modern vehicles control the fuel supply with an oxygen sensor feedback
system to maintain stoichiometry. Oxygen sensors are located typically
in the exhaust system upstream and downstream of the catalytic
converters. The front, or upstream, oxygen sensor is used generally for
fuel control. The rear, or downstream, oxygen sensor is used generally
for adjusting the front oxygen sensor signal as it drifts slightly with
age related deterioration--often referred to as fuel trimming--and for
onboard monitoring the catalyst system. Many vehicles use A/F sensors
in lieu of the more conventional oxygen sensors since A/F sensors
provide a precise reading of the actual air-fuel ratio.
    We expect that heavy-duty gasoline manufacturers will use both of
these types of sensors to optimize their emissions control strategies
and to satisfy many of the proposed heavy-duty OBD monitoring
requirements--fuel system monitoring, catalyst monitoring, EGR system
monitoring. Since exhaust gas sensors can be a critical component of an
engine's fuel and emissions control system, their proper performance
needs to be assured to maintain low emissions. Thus, any malfunction
that adversely affects the performance of any of these exhaust gas
sensors should be detected by the OBD system.
b. Exhaust Gas Sensor Monitoring Requirements
    We are proposing that the OBD system monitor the output signal,
response rate, and any other parameter that could affect emissions of
all primary (i.e., fuel control) exhaust gas sensors for malfunction.
Both the lean to rich and rich to lean response rates must be
monitored. In addition, we are proposing that the OBD system monitor
all secondary exhaust gas sensors (i.e., those used for fuel trimming
or as a monitoring device for another system) for proper output signal,
activity, and response rate. For engines equipped with heated exhaust
gas sensors, the OBD system would be required to monitor the sensor
heater for proper performance.
i. Primary Exhaust Gas Sensors
    We are proposing that the OBD system detect a malfunction prior to
any failure or deterioration of the exhaust gas sensor output voltage,
resistance, impedance, current, response rate, amplitude, offset, or
other characteristic(s) (including drift or bias corrected for by
secondary sensors) that would cause an engine's emissions to exceed the
emissions thresholds for ``other monitors'' as shown in Table II.C-1.
The OBD system would also be required to detect the following exhaust
gas sensor malfunctions:
     Those caused by either a lack of circuit continuity or
out-of-range values.
     Those where a sensor failure or deterioration causes the
fuel system to stop using that sensor as a feedback input (e.g., causes
default or open-loop operation).
     Those where the sensor output voltage, resistance,
impedance, current, amplitude, activity, or other characteristics are
no longer sufficient for use as an OBD system monitoring device (e.g.,
for catalyst monitoring).
ii. Secondary Exhaust Gas Sensors
    We are proposing that the OBD system detect a malfunction prior to
any failure or deterioration of the exhaust gas sensor voltage,
resistance, impedance, current, response rate, amplitude, offset, or
other characteristic(s) that would cause an engine's emissions to
exceed the emissions thresholds for ``other monitors'' as shown in
Table II.C-1. The OBD system would also be required to detect the
following exhaust gas sensor malfunctions:
     Those caused by either a lack of circuit continuity or
out-of-range values.
     Those where a sensor failure or deterioration causes the
fuel system to stop using that sensor as a feedback input (e.g., causes
default or open-loop operation).
     Those where the sensor output voltage, resistance,
impedance, current, amplitude, activity, or other characteristics are
no longer sufficient for use as an OBD system monitoring device (e.g.,
for catalyst monitoring).
iii. Exhaust Gas Sensor Heaters
    We are proposing that the OBD system detect a malfunction of the
sensor heater performance when the current or voltage drop in the
heater circuit is no longer within the manufacturer's specified limits
for normal operation (i.e., within the criteria required by the
component vendor for heater circuit performance at high mileage). The
manufacturer may use other malfunction criteria for heater performance
malfunctions. To do so, the manufacturer would be required to submit
data and/or engineering analyses that demonstrate that the monitoring
reliability and timeliness would be equivalent to the criteria stated
here.
    In addition, the OBD system would be required to detect
malfunctions of the heater circuit including open or short circuits
that conflict with the commanded state of the heater (e.g., shorted to
12 Volts when commanded to 0 Volts (ground)).
c. Exhaust Gas Sensor Monitoring Conditions
i. Primary Exhaust Gas Sensors
    We are proposing that manufacturers define the monitoring
conditions for primary exhaust gas sensor malfunctions causing
exceedance of the applicable thresholds and/or inability to perform as
an OBD monitoring device such that the minimum performance ratio
requirements discussed in section II.E would be met. For purposes of
tracking and reporting as required in section II.E, all such monitors
must be tracked separately but reported as a single set of values as
specified in section II.E.
    Monitoring for primary exhaust gas sensor malfunctions related to
circuit continuity, out-of-range, and open-loop operation must be done
continuously with the exception that manufacturers may disable
continuous exhaust gas sensor monitoring when an exhaust gas sensor
malfunction cannot be distinguished from other effects. As an example,
a manufacturer may disable monitoring for out-of-range on the low side
during conditions where fuel has been cut (i.e., shut off temporarily).
To do so, the manufacturer would have to submit data and/or engineering
analyses that demonstrate that a properly functioning sensor cannot be
distinguished from a malfunctioning sensor and that the disablement
interval is limited only to that necessary for avoiding a false
detection.
ii. Secondary Exhaust Gas Sensors
    We are proposing that manufacturers define the monitoring
conditions for secondary exhaust gas sensor malfunctions causing
exceedance of the applicable emissions thresholds, lack of circuit
continuity, and/or inability to perform as an OBD monitoring device
such that the minimum performance ratio requirements discussed in
section II.E would be met.
    Monitoring for secondary exhaust gas sensor malfunctions related to
out-of-

range and open loop operation must be done continuously with the
exception that manufacturers may disable continuous exhaust gas sensor
monitoring when an exhaust gas sensor malfunction cannot be
distinguished from other effects. As an example, a manufacturer may
disable monitoring for out-of-range on the low side during conditions
where fuel has been cut (i.e., shut off temporarily). To do so, the
manufacturer would have to submit data and/or engineering analyses that
demonstrate that a properly functioning sensor cannot be distinguished
from a malfunctioning sensor and that the disablement interval is
limited only to that necessary for avoiding a false detection.
iii. Sensor Heaters
    We are proposing that manufacturers define monitoring conditions
for sensor heater performance malfunctions such that the minimum
performance ratio requirements discussed in section II.E would be met.
Monitoring for sensor heater circuit malfunctions must be done
continuously.
d. Exhaust Gas Sensor MIL Illumination and DTC Storage
    We are proposing the general requirements for MIL illumination and
DTC storage as discussed in section II.A.2.

D. Monitoring Requirements and Timelines for Other Diesel and Gasoline
Systems

1. Variable Valve Timing and/or Control (VVT) System Monitoring
a. Background
    Variable valve timing (VVT) and/or control systems are used
primarily to optimize engine performance and have many advantages over
conventional valve control. Instead of opening and closing the valves
by fixed amounts and at fixed times, VVT controls can vary the timing
of valve opening/closing and vary the effective size of the valve
opening itself (in some systems) depending on the driving conditions
(e.g., high engine speed and load). This feature permits a better
compromise between performance, driveability, and emissions than
conventional systems. With more stringent NOX emission
standards being phased in, more vehicles are anticipated to use VVT. By
doing so, some exhaust gas can be retained in the combustion chamber
thereby reducing peak combustion temperatures and, hence,
NOX emissions (known as ``internal EGR'').
b. VVT and/or Control System Monitoring Requirements
    We are proposing that the OBD system monitor the VVT system on
engines so equipped for target error and slow response malfunctions.
The individual electronic components (e.g., actuators, valves, sensors)
that are used in the VVT system must be monitored in accordance with
the comprehensive components requirements in section II.D.4.
i. VVT Target Error Malfunctions
    We are proposing that the OBD system detect a malfunction prior to
any failure or deterioration in the capability of the VVT system to
achieve the commanded valve timing and/or control within a crank angle
and/or lift tolerance that would cause an engine's emissions to exceed
the emissions thresholds for ``other monitors'' as shown in Table II.B-
1 for diesel engines or Table II.C-1 for gasoline engines. For engines
in which no failure or deterioration of the VVT system could result in
an engine's emissions exceeding the applicable emissions thresholds,
the OBD system would have to detect a malfunction of the VVT system
when proper functional response of the system to computer commands does
not occur.
ii. VVT Slow Response Malfunctions
    We are proposing that the OBD system detect a malfunction prior to
any failure or deterioration in the capability of the VVT system to
achieve the commanded valve timing and/or control within a
manufacturer-specified time that would cause an engine's emissions to
exceed the emissions thresholds for ``other monitors'' as shown in
Table II.B-1 for diesel engines or Table II.C-1 for gasoline engines.
For engines in which no failure or deterioration of the VVT system
could result in an engine's emissions exceeding the applicable
emissions thresholds, the OBD system would have to detect a malfunction
of the VVT system when proper functional response of the system to
computer commands does not occur.
c. VVT and/or Control System Monitoring Conditions
    We are proposing that manufacturers define the monitoring
conditions for VVT target error or slow response malfunctions such that
the minimum performance ratio requirements discussed in section II.E
would be met with the exception that monitoring shall occur every time
the monitoring conditions are met during the driving cycle rather than
once per driving cycle as required for most monitors. For purposes of
tracking and reporting as required in section II.E, all monitors used
to detect all VVT related malfunctions would have to be tracked
separately but reported as a single set of values as specified in
section II.E.\42\
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    \42\ For specific components or systems that have multiple
monitors that are required to be reported (e.g., exhaust gas sensor
bank 1 may have multiple monitors for sensor response or other
sensor characteristics), the OBD system must separately track
numerators and denominators for each of the specific monitors and
report only the corresponding numerator and denominator for the
specific monitor that has the lowest numerical ratio. If two or more
specific monitors have identical ratios, the corresponding numerator
and denominator for the specific monitor that has the highest
denominator shall be reported for the specific component.
---------------------------------------------------------------------------

d. VVT and/or Control System MIL Illumination and DTC Storage
    We are proposing the general requirements for MIL illumination and
DTC storage as discussed in section II.A.2.
2. Engine Cooling System Monitoring
a. Background
    We are concerned about two elements of the engine cooling system.
These elements are the thermostat and the engine coolant temperature
sensor. Manufacturers typically use a thermostat to control the flow of
coolant through the radiator and around the engine. During a cold
engine start, the thermostat is closed typically which prevents the
flow of coolant and serves to promote more rapid warm-up of the engine.
As the coolant approaches a specific temperature, the thermostat begins
to open allowing circulation of coolant through the radiator and around
the engine. The thermostat then acts to regulate the coolant to the
specified temperature. If the temperature rises above the regulated
temperature, the thermostat opens further to allow more coolant to
circulate, thus reducing the temperature. If the temperature drops
below the regulated temperature, the thermostat partially closes to
reduce the amount of coolant circulating, thereby increasing the
temperature. If a thermostat malfunctions in such a manner that it does
not adequately restrict coolant flow during vehicle warm-up, an
increase in emissions could occur due to prolonged operation of the
vehicle at temperatures below the stabilized, warmed-up value. This is
particularly true at lower ambient temperatures--50 degrees Fahrenheit
and below--but not so low that they are rare in the U.S. Equally
important is that the engine coolant temperature is often used as an
enable criterion for many OBD monitors. If the engine's coolant
temperature does not reach the

manufacturer-specified warmed-up value, such monitors would be
effectively disabled, perhaps indefinitely, and would, therefore, never
detect malfunctions.
    Closely linked with the thermostat is the engine coolant
temperature (ECT) sensor. Manufacturers typically use an ECT sensor as
an input for many of the emission-related engine control systems. For
gasoline engines, the ECT sensor is often one of the most important
factors in determining when to begin closed-loop fuel control. If the
engine coolant does not warm-up sufficiently, closed-loop fuel control
is usually not engaged and the vehicle remains in open-loop fuel
control. Since open-loop fuel control does not provide the precision of
closed-loop control, the result is increased emissions levels. For
diesel engines, the ECT sensor is often used to engage closed-loop
control of the EGR system. Similar to closed-loop fuel control on
gasoline engines, if the coolant temperature does not warm up, closed-
loop control of the EGR system would not engage which would result in
increased emissions levels. In addition, for both gasoline and diesel
engines, the ECT sensor may be used to enable many of the monitors that
are being proposed. Such monitors would be effectively disabled and
incapable of detecting malfunctions should the ECT sensor itself
malfunction.
b. Engine Cooling System Monitoring Requirements
    We are proposing that the OBD system monitor the thermostat on
engines so equipped for proper operation. We are also proposing that
the OBD system monitor the ECT sensor for circuit continuity, out-of-
range values, and rationality faults. For engines that use an approach
other than the cooling system and ECT sensor--e.g., oil temperature,
cylinder head temperature--for an indication of engine operating
temperature for emission control purposes (e.g., to modify spark or
fuel injection timing or quantity), the manufacturer may forego cooling
system monitoring in favor of monitoring the components or systems used
in their approach. To do so, the manufacturer would be required to
submit data and/or engineering analyses that demonstrate that their
monitoring plan is as reliable and effective as the monitoring required
for the engine cooling system.
i. Thermostat Monitoring Requirements
    We are proposing that the OBD system detect a thermostat
malfunction if, within the manufacturer specified time interval
following engine start, any of the following conditions occur:
     The coolant temperature does not reach the highest
temperature required by the OBD system to enable other diagnostics;
     The coolant temperature does not reach a warmed-up
temperature within 20 degrees Fahrenheit of the manufacturer's nominal
thermostat regulating temperature. The manufacturer may use a lower
temperature for this criterion provided the manufacturer can
demonstrate that the fuel, spark timing, and/or other coolant
temperature-based modification to the engine control strategies would
not cause an emissions increase greater than or equal to 50 percent of
any of the applicable emissions standards.
    The time interval specified by the manufacturer would have to be
supported by the manufacturer via data and/or engineering analyses
demonstrating that it provides robust monitoring and minimizes the
likelihood of other OBD monitors being disabled. The manufacturer may
use alternative malfunction criteria that are a function of temperature
at engine start on engines that do not reach the temperatures specified
in the malfunction criteria when the thermostat is functioning
properly. To do so, the manufacturer would be required to submit data
and/or engineering analyses that demonstrate that a properly operating
system does not reach the specified temperatures and that the
possibility is minimized for cooling system malfunctions to go
undetected and disable other OBD monitors. In some cases, a
manufacturer may forgo thermostat monitoring if the manufacturer can
demonstrate that a malfunctioning thermostat cannot cause a measurable
increase in emissions during any reasonable driving condition nor cause
any disablement of other OBD monitors.
ii. Engine Coolant Temperature Sensor Monitoring Requirements
    We are proposing that the OBD system detect an ECT sensor
malfunction when a lack of circuit continuity or an out-of-range value
occurs. We are also proposing that the OBD system detect if, within the
manufacturer specified time interval following engine start, the ECT
sensor does not achieve the highest stabilized minimum temperature that
is needed to initiate closed-loop/feedback control of all affected
emission control systems (e.g., fuel system, EGR system). The
manufacturer specified time interval would have to be a function of the
engine coolant temperature and/or intake air temperature at startup.
The manufacturer time interval would also have to be supported by the
manufacturer via data and/or engineering analyses demonstrating that it
provides robust monitoring and minimizes the likelihood of other OBD
monitors being disabled. Manufacturers may forego the requirement to
detect the ``time to closed loop/feedback enable temperature''
malfunction if the manufacturer does not use engine coolant temperature
or the ECT sensor to enable closed-loop/feedback control of any
emission control systems.
    We are also proposing that, to the extent feasible when using all
available information, the OBD system must detect a malfunction if the
ECT sensor inappropriately indicates a temperature below the highest
minimum enable temperature required by the OBD system to enable other
monitors. For example, an OBD system that requires an engine coolant
temperature greater than 140 degrees Fahrenheit prior to enabling an
OBD monitor must detect malfunctions that cause the ECT sensor to
indicate inappropriately a temperature below 140 degrees Fahrenheit.
Manufacturers may forego such monitoring within temperature regions in
which the thermostat monitor or the ECT sensor ``time to reach closed-
loop/feedback enable temperature'' monitor would detect this ``stuck in
a range below the highest minimum enable temperature'' ECT sensor
malfunction.
    Lastly, we are proposing that, to the extent feasible when using
all available information, the OBD system must detect a malfunction if
the ECT sensor inappropriately indicates a temperature above the lowest
maximum enable temperature required by the OBD system to enable other
monitors. For example, an OBD system that requires an engine coolant
temperature less than 90 degrees Fahrenheit at startup prior to
enabling an OBD monitor must detect malfunctions that cause the ECT
sensor to indicate inappropriately a temperature above 90 degrees
Fahrenheit. Manufacturers may forego such monitoring within temperature
regions in which the thermostat monitor, the ECT sensor ``time to reach
closed-loop/feedback enable temperature'' monitor, or the ECT sensor
``stuck in a range below the highest minimum enable temperature''
monitor would detect this ECT sensor ``stuck in a range above the
lowest maximum enable temperature'' ECT sensor malfunction. The
manufacturer may also forego such monitoring if the MIL would be
illuminated for entering a ``limp home'' or default mode of

operation--e.g., for an over temperature protection strategy--as