[cir] DEF Line Heater Control Outputs
[cir] Speed and output shaft torque consistent with 40 CFR 1036.115(d)

     For Spark Ignition Engines:

[cir] Air/Fuel Enrichment Enable flags: Throttle based, Load based,
Catalyst protection based
[cir] Percent of time not in stoichiometric operation (including per
trip and since new)

    One of the more useful features in the CARB OBD program for
diagnosing and repairing emissions components is the requirement for
``freeze frame'' data to be stored by the system. To comply with this
requirement, manufacturers must capture and store certain data
parameters (e.g., vehicle operating conditions such as the
NOX sensor output reading) within 10 seconds of the system
detecting a malfunction. The purpose of storing this data is in part to
record the likely area of malfunction. EPA is finalizing a requirement
in 40 CFR 1036.110(b)(8) to require that manufacturers capture the
following elements as freeze frame data: Those data parameters
specified in 1971.1(h)(4.2.3)(E), 1971.1(h)(4.2.3)(F), and
1971.1(h)(4.2.3)(G). We are also specifying that these additional
parameters would be added according to the specifications in 13 CCR
1971.1(h)(4.3). EPA believes this is essential information to make
available to operators for proper maintenance.
iv. Demonstration Testing Requirements
    Existing requirements of 40 CFR 86.010-18(l) and 13 CCR 1971.1(l)
specify the number of test engines for which a manufacturer must submit
monitoring system demonstration emissions data. Specifically, a
manufacturer certifying one to five engine families in a given model
year must provide emissions test data for a single test engine from one
engine rating, a manufacturer certifying six to ten engine families in
a given model year must provide emissions test data for a single test
engine from two different engine ratings, and a manufacturer certifying
eleven or more engine families in a given model year must provide
emissions test data for a single test engine from three different
engine ratings.
    EPA received supportive and adverse comment on a proposed
flexibility to

reduce redundant demonstration testing requirements for certain engines
where an OBD system designed to comply with California OBD requirements
is being used in both a CARB proposed family and a proposed EPA-only
family and the two families are also identical in all aspects material
to expected emission characteristics. EPA issued guidance last year on
this issue.\361\ We are finalizing as proposed to codify this guidance
as a provision, subject to certain information submission requirements
for EPA to evaluate if this provision's requirements have been met, for
model years 2027 and later engines in 40 CFR 1036.110(b)(11).
Manufacturers may also use the flexibility in earlier model years. More
specifically, we are finalizing the provision as proposed to count two
equivalent engines families as one for the purposes of determining OBD
demonstration testing requirements, where equivalent means they are
identical in all aspects material to emission characteristics, as such,
testing is not necessary to ensure a robust OBD program. 40 CFR
1036.110(b)(11) requires manufacturers to submit additional information
as needed to demonstrate that the engines meet the requirements of 40
CFR 1036.110 that are not covered by the California Executive order, as
well as results from any testing performed for certifying engine
families (including equivalent engine families) with the California Air
Resources Board and any additional information we request as needed to
evaluate whether the requirements of this provision are met.
---------------------------------------------------------------------------

    \361\ EPA Guidance Document CD-2021-04 (HD Highway), April 26,
2021, ``Information on OBD Monitoring System Demonstration for Pairs
of EPA and CARB Families Identical in All Aspects Other Than
Warranty.'' Available here:  https://iaspub.epa.gov/otaqpub/display_file.jsp?docid=52574&flag=1.
---------------------------------------------------------------------------

    We took comment on and are finalizing language that this
flexibility will apply for cases where equivalent engine families also
have different inducement strategies. We are aware that the auxiliary
emission control devices (AECDs) needed to implement the engine
derating associated with inducements do not affect engine calibrations
in a way that would prevent OBD systems from detecting when emissions
exceed specified levels. Rather, those AECDs simply limit the range of
engine operation that is available to the driver. Thus, testing of
different inducement strategies in these AECDs would also not be
necessary to ensure a robust OBD program and we would consider such
differences between engines to not be material to emission
characteristics relevant to these OBD testing requirements. Any
difference in impacts between the engines would be a consequence of the
driver's response to the inducement itself, which could also occur even
with the same inducement strategy, rather than a difference in the
functioning of the OBD systems in the engines. In that way, inducements
are analogous to warranty for purposes of counting engine families for
OBD testing requirements. See section 8 of the Response to Comments for
details on the comments received and EPA's responses.
v. Use of CARB OBD Approval for EPA OBD Certification
    Existing EPA OBD regulations allow manufacturers seeking an EPA
certificate of conformity to comply with the Federal OBD requirements
by demonstrating to EPA how the OBD system they have designed to comply
with California OBD requirements also meets the intent behind Federal
OBD requirements, as long as the manufacturer complies with certain
certification documentation requirements. EPA has implemented these
requirements by allowing a manufacturer to submit an OBD approval
letter from CARB for the equivalent engine family where a manufacturer
can demonstrate that the CARB OBD program has met the intent of the EPA
OBD program. In other words, EPA has interpreted these requirements to
allow OBD approval from CARB to be submitted to EPA for approval. We
are finalizing as proposed to migrate the language from 40 CFR 86.010-
18(a)(5) to 40 CFR 1036.110(b) to allow manufacturers to continue to
use a CARB OBD approval letter to demonstrate compliance with Federal
OBD regulations for an equivalent engine family where manufacturers can
demonstrate that the CARB OBD program has met the intent of the EPA OBD
program.
    To demonstrate that your engine meets the intent of EPA OBD
requirements, we are finalizing as proposed that the OBD system must
address all the provisions described in 40 CFR 1036.110(b) and (c) and
adding clarification in 40 CFR 1036.110(b) that manufacturers must
submit information demonstrating that all EPA requirements are met. In
the case where a manufacturer chooses not to include information
showing compliance with additional EPA OBD requirements in their CARB
certification package (e.g., not including the additional EPA data
parameters in their CARB certification documentation), EPA expects
manufacturers to provide separate documentation along with the CARB OBD
approval letter to show they have met all EPA OBD requirements. This
process also applies in potential future cases where CARB has further
modified their OBD requirements such that they are different from but
meet the intent of existing EPA OBD requirements. EPA expects
manufacturers to submit documentation as is currently required by 40
CFR 86.010-18(m)(3), detailing how the system meets the intent of EPA
OBD requirements and information on any system deficiencies. As a part
of this update to EPA OBD regulations, we are clarifying as proposed in
40 CFR 1036.110(b)(11)(iii) that we can request that manufacturers send
us information needed for us to evaluate how they meet the intent of
our OBD program using this pathway. This would often mean sending EPA a
copy of documents submitted to CARB during the certification process.
vi. Use of the SAE J1979-2 Communications Protocol
    In a February 2020 workshop, CARB indicated their intent to propose
allowing the use of Unified Diagnostic Services (``UDS'') through the
SAE J1979-2 communications protocol for heavy-duty OBD with an optional
implementation as early as MY 2023.\362 363\ The CARB OBD update that
includes this UDS proposal has not yet been finalized, but was
submitted to California's Office of Administrative Law for approval in
July of 2022.\364\ CARB stated that engine manufacturers are concerned
about the limited number of remaining undefined 2-byte diagnostic
trouble codes (``DTC'') and the need for additional DTCs for hybrid
vehicles. SAE J1979-2 provides 3-byte DTCs, significantly increasing
the number of DTCs that can be defined. In addition, this change would
provide additional features for data access that improve the usefulness
of generic scan tools to repair vehicles.
---------------------------------------------------------------------------

    \362\ SAE J1979-2 was issued on April 22, 2021 and is available
here: https://www.sae.org/standards/content/j1979-2_202104/.
    \363\ CARB Workshop for 2020 OBD Regulations Update, February
27, 2020. Available here: https://ww3.arb.ca.gov/msprog/obdprog/obd_feb2020wspresentation.pdf.
    \364\ CARB Proposed Revisions to the On-Board Diagnostic System
Requirements and Associated Enforcement Provisions for Passenger
Cars, Light-Duty Trucks, Medium-Duty Vehicles and Engines, and
Heavy-Duty Engines, available: https://ww2.arb.ca.gov/rulemaking/2021/obd2021.
---------------------------------------------------------------------------

    This update has not been finalized by CARB in time for us to
include it in this final rule. In consideration of manufacturers who
want to certify their engine families in the future for

nationwide use, and after consideration of expected environmental
benefits associated with the use of this updated protocol, we are
finalizing as proposed a process for reviewing and approving
manufacturers' requests to comply using the alternative communications
protocol.
    While EPA believes our existing requirements in 40 CFR 86.010-
18(a)(5) allow us to accept OBD systems using SAE J1979-2 that have
been approved by CARB, there may be OEMs that want to obtain an EPA-
only certificate (i.e., does not include certification to California
standards) for engines that do not have CARB OBD approval for MYs prior
to MY 2027 (i.e., prior to when the 40 CFR part 1036 OBD provisions of
this final rule become mandatory). EPA is finalizing as proposed to
allow the use of SAE J1979-2 for manufacturers seeking EPA OBD
approval. We are adopting this as an interim provision in 40 CFR
1036.150(v) to address the immediate concern for model year 2026 and
earlier engines. Once EPA's updated OBD requirements are in effect for
MY 2027, we expect to be able to allow the use of SAE J1979-2 based on
the final language in 40 CFR 1036.110(b); however, we do not specify an
end date for the provision in 40 CFR 1036.150(v) to make sure there is
a smooth transition toward using SAE J1979-2 for model years 2027 and
later. This provides manufacturers the option to upgrade their OBD
protocol to significantly increase the amount of OBD data available to
owners and repair facilities.
    CAA section 202(m)(4)(C) requires that the output of the data from
the emission control diagnostic system through such connectors shall be
usable without the need for any unique decoding information or device,
and it is not expected that the use of SAE J1979-2 would conflict with
this requirement. Further, CAA section 202(m)(5) requires manufacturers
to provide promptly to any person engaged in the repairing or servicing
of motor vehicles or motor vehicle engines, and the Administrator for
use by any such persons, with any and all information needed to make
use of the emission control diagnostics system prescribed under this
subsection and such other information including instructions for making
emission related diagnosis and repairs. Manufacturers that voluntarily
use J1979-2 as early as MY 2022 under interim provision 40 CFR
1036.150(v) would need to provide access to systems using this
alternative protocol at that time and meet all the relevant
requirements in 40 CFR 86.010-18 and 1036.110. EPA did not receive
adverse comment on the availability of tools that can read the new
protocol from manufacturers or tool providers. CARB commented that
staff anticipates tool vendors will be able to fully support the SAE
J1979-2 protocol at a fair and reasonable price for the vehicle repair
industry and consumers.
2. Cost Impacts
    Heavy-duty engine manufacturers currently certify their engines to
meet CARB's OBD regulations before obtaining EPA certification for a
50-state OBD approval. We anticipate most manufacturers will continue
to certify with CARB and that they will certify to CARB's 2019 updated
OBD regulations well in advance of the EPA program taking effect;
therefore, we anticipate the incorporation by reference of CARB's 2019
OBD requirements will not result in any additional costs. EPA does not
believe the additional OBD requirements described here will result in
any significant costs, as there are no requirements for: New monitors,
new data parameters, new hardware, or new testing included in this
rule. However, EPA has accounted for possible additional costs that may
result from the final expanded list of public OBD parameters in the
``Research and Development Costs'' of our cost analysis in Section V.
EPA recognizes that there could be cost savings associated with reduced
OBD testing requirements under final 40 CFR 1036.110(c)(11). For
example, cost savings could come from the provision to not count engine
families certified separately by EPA and CARB, but otherwise identical
in all aspects material to expected emission characteristics, as
different families when determining OBD demonstration testing (see
section IV.C.1.iv of this document for further discussion on this
provision). This potential reduction in demonstration testing burden
could reduce costs such as labor and test cell time. However,
manufacturers may choose not to certify engine families in this manner
which would not translate to cost savings. Therefore, given the
uncertainty in the potential for savings, we did not quantify the costs
savings associated with this final provision.
D. Inducements
    Manufacturers have deployed urea-based SCR systems to meet the
existing heavy-duty engine emission standards. EPA anticipates that
manufacturers will continue to use this technology to meet the new
NOX standards finalized in this rule. SCR is very different
from other emission control technologies in that it requires operators
to maintain an adequate supply of diesel exhaust fluid (DEF), which is
generally a water-based solution with 32.5 percent urea. Operating an
SCR-equipped engine without DEF or certain components like an SCR
catalyst could cause NOX emissions to increase to levels
comparable to having no NOX controls at all.
    The proposed rule described two key aspects of how our regulations
currently require manufacturers to ensure engines will operate with an
adequate supply of high-quality DEF, which we proposed to update and
further codify. First, manufacturers currently must demonstrate
compliance with our critical emissions-related schedule maintenance
requirements, including 40 CFR 86.004-25(b). EPA has approved DEF
refills as part of manufacturers' scheduled maintenance. EPA's approval
is conditioned on manufacturers demonstrating that operators are
reasonably likely to perform such maintenance. Manufacturers have
consistently made this demonstration by designing their engines to go
into a disabled mode that decreases a vehicle's maximum speed if the
engine detects that operators are failing to provide an adequate supply
of DEF. More specifically, manufacturers have generally complied by
programming engines to restrict peak vehicle speeds after detecting
that such maintenance has not been performed or detecting that
tampering with the SCR system may have occurred. We refer to this
strategy of derating engine power and vehicle speed as an
``inducement.''
    Second, EPA's current regulations in 40 CFR 86.094-22(e) require
that manufacturers comply with emission standards over the full
adjustable range of ``adjustable parameters,'' and that, in determining
the parameters subject to adjustment, EPA considers the likelihood that
settings other than the manufacturer's recommended setting will occur
in-use, including the effect of settings other than the manufacturer's
recommended settings on engine performance. We have historically
considered DEF level and quality as parameters that can be physically
adjusted and may significantly affect emissions. EPA generally has
approved manufacturers strategies consistent with guidance that
described recommendations on ways manufacturers could meet adjustable
parameter requirements when using SCR systems.\365\ This guidance
states that manufacturers should demonstrate that operators are being
made aware that DEF needs to be replaced through warnings and vehicle
performance

deterioration that should not create undue safety concerns but be
onerous enough to discourage drivers from operating without DEF (i.e.,
through inducement). See the proposed rule preamble for further
background and discussion of the basis of EPA's proposed inducement
regulations.
---------------------------------------------------------------------------

    \365\ See CISD-09-04 REVISED.
---------------------------------------------------------------------------

    With some modification from the proposal, EPA is adopting final
inducement regulations in this final rule. The regulatory provisions
also include changes compared to existing inducement guidance after
consideration of manufacturer designs and operator experiences with SCR
over the last several years. The inducement requirements included in
this final rule supersede the existing guidance and are mandatory
beginning in MY 2027 and voluntary prior to that and are intended to-
     Ensure that all critical emission-related scheduled
maintenance has a reasonable likelihood of being performed while also
deterring tampering of the SCR system.
     Set an appropriate inducement speed derating schedule that
reflects experience gained over the past decade with SCR systems.
     Recognize the diversity of the real-world fleet with
derate schedules that are tailored to a vehicle's operating
characteristics.
     Improve the type and amount of information operators
receive from the vehicle to both understand inducement actions and to
help avoid or quickly remedy a problem that is causing an inducement.
     Allow operators to perform an inducement reset by using a
generic scan tool or allowing for the engine to self-heal during normal
driving.
     Address operator frustration with false inducements and
low inducement speed restrictions that occur quickly, in part due to
concern that such frustration may potentially lead to in-use tampering
of the SCR system.
    This final rule includes several changes from the proposed rule
after consideration of numerous comments. See section 8 of the Response
to Comments for the detailed comments and EPA's response to those
comments, including further discussion of the changes in the final rule
compared to the proposed rule. As an overview, EPA is adopting as a
maintenance requirement, as proposed, in 40 CFR 1036.125(a)(1) that
manufacturers must meet the specifications in new 40 CFR 1036.111,
which contains requirements for inducements related to SCR, to
demonstrate that timely replenishment with high-quality DEF is
reasonably likely to occur on in-use engines and that adjustable
parameter requirements will be met. Specifically, EPA is finalizing as
proposed to specify in 40 CFR 1036.115(f) that DEF supply and DEF
quality are adjustable parameters. Regarding DEF supply, we are
finalizing as proposed that the physically adjustable range includes
any amount of DEF that the engine's diagnostic system does not
recognize as a fault condition under new 40 CFR 1036.111. We are
adopting a requirement under new 40 CFR 1036.115(i) for manufacturers
to size DEF tanks corresponding to refueling events, which is
consistent with the regulation we are replacing under 40 CFR 86.004-
25(b)(4)(v). Under the final requirements, manufacturers can no longer
use the alternative option in 40 CFR 86.004-25(b)(6)(ii)(F) to
demonstrate high-quality DEF replenishment is reasonably likely to be
performed in use. As described in the proposed rule, EPA plans to
continue to rely on the existing guidance in CD-13-13 that describes
how manufacturers of heavy-duty highway engines determine the
practically adjustable range for DEF quality. We inadvertently proposed
to require that manufacturers use the physically adjustable range for
DEF quality as the basis for defining a fault condition for inducements
under 40 CFR 1036.111. Since we intended for the existing guidance to
addresses issues related to the physically adjustable range for DEF
quality, we are not finalizing the proposed provision in 40 CFR
1036.115(f)(2) for DEF quality. EPA intends further consider the
relationship between inducements and the practically adjustable range
for DEF quality and may consider updating this guidance in the future.
    EPA is adopting requirements that inducements be triggered for
three types of fault conditions: (1) DEF supply is low, (2) DEF quality
does not meet manufacturer specifications, or (3) tampering with the
SCR system. EPA is not taking final action at this time on the proposed
requirement for manufacturers to include a NOX override to
prevent false inducements. After consideration of public comments, the
final inducement provisions at 40 CFR 1036.111 include updates from the
proposed inducement schedules; more specifically, EPA is adopting
separate inducement schedules for low-, medium-, and high-speed
vehicles. EPA is also finalizing requirements for manufacturers to
improve information provided to operators regarding inducements. The
final rule also includes a requirement for manufacturers to design
their engines to remove inducements after proper repairs are made,
through self-healing or with the use of a generic scan tool to ensure
that operators have performed the proper maintenance.
    These requirements apply starting in MY 2027, though manufacturers
may optionally comply with these 40 CFR part 1036 requirements in lieu
of provisions that apply under 40 CFR part 86 early. The following
sections describe the inducement requirements for the final rule in
greater detail.
1. Inducement Triggers
    Three types of fault conditions trigger inducements under 40 CFR
1036.111. The first triggering condition is DEF quantity. Specifically,
we require that SCR-equipped engines trigger an inducement when the
amount of DEF in the tank has been reduced to a level corresponding to
three remaining hours of engine operation. This triggering condition
ensures that operators will be compelled to perform the necessary
maintenance before the DEF supply runs out, which would cause emissions
to increase significantly.
    The second triggering condition is DEF quality failing to meet
manufacturer concentration specifications. This triggering condition
ensures high quality DEF is used.
    Third, EPA is requiring inducements to ensure that SCR systems are
designed to be tamper-resistant. We are requiring that manufacturers
design their engines to monitor for and trigger an inducement for open-
circuit fault conditions for the following components: (1) DEF tank
level sensor, (2) DEF pump, (3) DEF quality sensor, (4) SCR wiring
harness, (5) NOX sensors, (6) DEF dosing valve, (7) DEF tank
heater, (8) DEF tank temperature sensor, and (9) aftertreatment control
module (ACM). EPA is also requiring that manufacturers monitor for and
trigger an inducement if the OBD system has any signal indicating that
a catalyst is missing (see OBD requirements for this monitor in 13 CCR
1971.1(i)(3.1.6)). This list is the same as the list from the proposed
rule, with two exceptions after consideration of comments. First, we
are adding the DEF tank temperature sensor in the final rule. This
additional sensor is on par with the DEF tank heater for ensuring that
SCR systems are capable of monitoring for freezing conditions. Second,
in consideration of comment, we are removing blocked DEF lines or
dosing valves as a triggering condition because such a condition could
be caused by crystallized DEF rather than any operator action and thus
is not directly related to protecting against tampering with the SCR-
system. We believe this standardized list of required

tampering inducement triggers will be important for owners, operators,
and fleets in repairing their vehicles by avoiding excessive cost and
time to determine the reason for inducement.
2. Derate Schedule
    We are finalizing a different set of schedules than we proposed.
First, we are adding a new category for medium-speed vehicles. Second,
we are adjusting the low-speed category to have a lower final speed
compared to the proposal and a lower average operating speed to
identify this category. Third, we increased the average operating speed
that qualifies a vehicle to be in the high-speed category. We are
adopting derate schedules for low-, medium- and high-speed vehicles as
shown in Table IV-13. Similar to the proposal, we differentiate these
three vehicle categories based on a vehicle's calculated average speed
for the preceding 30 hours of non-idle operation. Low-speed vehicles
are those with an average operating speed below 15 mph. Medium-speed
vehicles are those with average operating speeds at or above 15 and
below 25 mph. High-speed vehicles are those with average operating
speeds at or above 25 mph. Excluding idle from the calculation of
vehicle speed allows us to more effectively evaluate each vehicle's
speed profile; in contrast, time spent at idle would not help to give
an indication of a vehicle's operating characteristics for purposes of
selecting the appropriate derate schedule. EPA chose these final speeds
after consideration of stakeholder comments (see section 8.3 of the
Response to Comments for further information on comments received) and
an updated analysis of real-world vehicle speed activity data from the
FleetDNA database maintained by the National Renewable Energy
Laboratory (NREL).366 367 Our analyses provided us with
insight into the optimum way to characterize vehicles in a way to
ensure these categories received appropriate inducements that would be
neither ineffective nor overly restrictive.
---------------------------------------------------------------------------

    \366\ EPA's original analysis of NREL data can be found here:
Miller, Neil; Kopin, Amy. Memorandum to docket EPA-HQ-OAR-2019-0055-
0981. ``Review and analysis of vehicle speed activity data from the
FleetDNA database.'' October 1, 2021.
    \367\ EPA's updated analysis of NREL data can be found here:
Miller, Neil; Kopin, Amy. Memorandum to docket EPA-HQ-OAR-2019-0055.
``Updated review and analysis of vehicle speed activity data from
the FleetDNA database.'' October 13, 2022.

                                                            Table IV-13--Inducement Schedules
--------------------------------------------------------------------------------------------------------------------------------------------------------
                           High-speed vehicles                                     Medium-speed vehicles                    Low-speed vehicles
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                      Maximum speed (mi/   Hours of non-idle  Maximum speed (mi/   Hours of non-idle  Maximum speed (mi/
         Hours of non-idle engine operation                   hr)          engine operation           hr)          engine operation           hr)
--------------------------------------------------------------------------------------------------------------------------------------------------------
0...................................................                  65                   0                  55                   0                  45
6...................................................                  60                   6                  50                   5                  40
12..................................................                  55                  12                  45                  10                  35
60..................................................                  50                  45                  40                  30                  25
86..................................................                  45                  70                  35  ..................  ..................
119.................................................                  40                  90                  25  ..................  ..................
144.................................................                  35  ..................  ..................  ..................  ..................
164.................................................                  25  ..................  ..................  ..................  ..................
--------------------------------------------------------------------------------------------------------------------------------------------------------

    The derate schedule for each vehicle category is set up with
progressively increasing severity to induce the owner or operator to
efficiently address conditions that trigger inducements. Table IV-13
shows the derate schedules in cumulative hours. The initial inducement
applies immediately when the OBD system detects any of the triggering
fault conditions identified in section IV.D.1. The inducement schedule
then steps down over time to result in the final inducement speed
corresponding to each vehicle category. The inducement schedule
includes a gradual transition (1mph every 5 minutes) at the beginning
of each step of derate and prior to any repeat inducement occurring
after a failed repair to avoid abrupt changes, as the step down in
derate speeds in the schedules will be implemented while the vehicle is
in motion. Inducements are intended to deteriorate vehicle performance
to a point unacceptable for typical driving in a manner that is safe
but onerous enough to discourage vehicles from being operated (i.e.,
impact the ability to perform work), such that operators will be
compelled to replenish the DEF tank with high-quality DEF and not
tamper with the SCR system's ability to detect whether there is
adequate high-quality DEF. To this end, as explained in the proposal,
our analyses of vehicle operational data from NREL show that even
vehicles whose operation is focused on local or intracity travel depend
on frequently operating at highway speeds to complete commercial
work.\368\ Vehicles in an inducement under the schedules we are
finalizing would not be able to maintain commercial functions. Our
analysis of the NREL data also show that even medium- and low-speed
vehicles travel at speeds up to 70 mph and indicate that it is likely
regular highway travel is critical for low-speed vehicles to complete
their work; for example, refuse trucks need to drop off collected waste
at a landfill or transfer station before returning to neighborhoods.
---------------------------------------------------------------------------

    \368\ EPA's updated analysis of NREL data can be found here:
Miller, Neil; Kopin, Amy. Memorandum to docket EPA-HQ-OAR-2019-0055.
``Updated review and analysis of vehicle speed activity data from
the FleetDNA database.'' October 13, 2022.
---------------------------------------------------------------------------

    Motorcoach operators submitted comments describing a greater
sensitivity to any speed derate because of a much greater
responsibility for carrying people safely to their intended
destinations over longer distances, including their role in emergency
response and national defense operations. After consideration of these
comments, we are allowing manufacturers to design and produce engines
that will be installed in motorcoaches with an alternative derate
schedule that starts with a 65 mi/hr derate when a fault condition is
first detected, steps down to 50 mi/hr after 80 hours, and concludes
with a final derate speed of 25 mi/hr after 180 hours of non-idle
operation. EPA is defining motorcoaches in 40 CFR 1036.801 to include
buses that are designed to travel long distances with row seating for
at least 30 passengers. This is intended to include charter services
available to the general public.
    Comments on the proposed inducement policy ranged from

objecting to any speed restrictions to advocating that we adopt a 5 mph
final derate speed. Some commenters supported the proposed rule, and
some commenters asserted that decreasing final derate speeds would
provide for greater assurance that operators would perform the
necessary maintenance. There was a similar range of comments regarding
the time specified for escalating the speed restrictions, with some
commenters agreeing with the proposed schedule, and other commenters
suggesting substantially more or less time.
    We made several changes from proposal after consideration of
comments, including three main changes. First, as noted in the
preceding paragraphs, the final rule includes a medium-speed vehicle
category. This allows us to adjust the qualifying criterion for high-
speed vehicles to finalize a derate schedule similar to that proposed
for vehicles that are clearly operating mostly on interstate highways
over long distances. Similarly, the added vehicle category allows us to
adjust the qualifying criterion for low-speed vehicles and adopt an
appropriately more restrictive final derate schedule for those vehicles
that are operating at lower speeds in local service.
    Second, we developed unique schedules for escalating the speed
restrictions for medium-speed and low-speed vehicles; this change was
based on the expectation that vehicles with lower average speeds spend
less time operating at highway speeds characteristic of inter-city
driving and will therefore not need to travel substantial distances to
return home for scheduling repair.
    Third, we added derate speeds that go beyond the first four stages
of derating that we proposed for high-speed vehicles, essentially
reducing the final inducement speeds for all vehicles to be the same as
low-speed vehicles. In other words, as shown in Table IV-13, both high-
and medium-speed vehicles eventually derate to the same speeds as low-
speed vehicles, after additional transition time after the derate
begins. For example, the final derate schedule for high-speed vehicles
goes through the proposed four derate stages for high-speed vehicles.
At the fifth derate stage the vehicle begins to be treated like a
medium-speed vehicle, starting at the third derate stage for medium-
speed vehicles and progressing through the fifth derate stage for
medium-speed vehicles. At the fifth derate stage the vehicle begins to
be treated like a low-speed vehicle, similarly starting at the third
derate stage for low-speed vehicles. A similar step-down approach
applies for medium-speed vehicles, transitioning down to the derate
stages for low-speed vehicles. This progression is intended to address
the concern that vehicle owners might reassign vehicles in their fleet
to lower-speed service, or sell vehicles to someone who would use the
vehicle for different purposes that don't depend on higher-speed
operations. Our assessment is that the NREL data show that no matter
what category vehicles are, they do not travel exclusively at or below
25 mph, indicating that vehicles derated to 25 mph cannot be operated
commercially.
    For the simplest type of maintenance, DEF refills, we fully expect
that the initial stage of derated vehicle speed will be sufficient to
compel vehicle operators to meet their maintenance obligations. We
expect operators will add DEF routinely to avoid inducements; however,
inducements begin three hours prior to the DEF tank being empty to
better ensure operation with an empty DEF tank is avoided.
    We expect that the derate schedules in this final rule will be
fully effective in compelling operators to perform needed maintenance.
This effectiveness will be comparable to the current approach under
existing guidance, but will reduce operating costs to operators. We
believe this measured approach will also result in lower tampering
rates involving time.
3. Driver Information
    In addition to the driver information requirements we are adopting
to improve serviceability and OBD (see section IV.B.3 and IV.C.1.iii
respectively of this preamble for more details on these provisions), we
are also adopting improved driver information requirements for
inducements. Specifically, we are adopting as proposed the requirement
for manufacturers to increase the amount of information provided to the
driver about inducements, including: (1) The condition causing the
derate (i.e., DEF quality, DEF quantity or tampering), (2) the fault
code and description of the code associated with the inducement, (3)
the current derate speed restriction, (4) hours until the next derate
speed decrease, and (5) what the next derate speed will be. It is
critical that operators have clear and ready access to information
regarding inducements to reduce concerns over progressive engine
derates (which can lead to motivations to tamper) as well as to allow
operators to make timely informed decisions, especially since
inducements are used by manufacturers to demonstrate that critical
emissions-related maintenance is reasonably likely to occur in-use. We
note that we are finalizing this requirement at 40 CFR 1036.110(c), in
a different regulatory section than proposed; however, the substance of
the requirement is the same as at proposal.
    EPA is requiring that all inducement-related diagnostic data
parameters be made available with generic scan tools to help operators
promptly respond when the engine detects fault condition requiring
repair or other maintenance (see section IV.C.1.iii. for further
information).
4. Clearing an Inducement Condition
    Following restorative maintenance, EPA is requiring that the engine
would allow the vehicle to self-heal if it confirms that the fault
condition is resolved. The engine would then remove the inducement,
which would allow the vehicle to resume unrestricted engine operation.
EPA is also requiring that generic scan tools be able to remove an
inducement condition after a successful repair. After clearing
inducement-related fault codes, all fault codes are subject to
immediate reevaluation that would lead to resuming the derate schedule
where it was at the time the codes were cleared if the fault persists.
Therefore, there is no need to limit the number of times a scan tool
can clear codes. Use of a generic scan tool to clear inducements would
allow owners who repair vehicles outside of commercial facilities to
complete the repair without delay (e.g., flushing and refilling a DEF
tank where contaminated DEF was discovered). However, if the same fault
condition repeats within 40 hours of engine operation (e.g., in
response to a DEF quantity fault an owner adds a small but insufficient
quantity of DEF), this will be considered a repeat faut. In response to
a repeat fault, the system will immediately resume the derate at the
same point in the derate schedule when the original fault was
deactivated. This is less time than the 80 hours EPA proposed in the
NPRM, but it is consistent with existing EPA guidance. After
consideration of comments, we believe that the shorter interval is long
enough to give a reliable confirmation that a repair has properly
addressed the fault condition, and are concerned that 80 hours would
risk treating an unrelated occurrence of a fault condition as if it
were a continuation of the same fault.
    EPA is not finalizing the proposed provision that an inducement
schedule is applied and tracked independently for each fault if
multiple fault conditions are detected due to the software complexity
for the

manufacturer in applying and tracking the occurrence of multiple derate
schedules. Section 4 of the Response to Comments for further discussion
of EPA's thinking to assist manufacturers regarding consideration for
programming diagnostic systems to handle overlapping fault conditions.
5. Further Considerations
    EPA is not taking final action at this time on the proposed
NOX override provision, which was proposed to prevent speed
derates for fault conditions that are caused by component failures if
the catalyst is nevertheless functioning normally. We received comments
describing concerns with our proposed methodology, including the
reliability of NOX sensors and use of OBD REAL
NOX data, and concerns that reliance in this way on the
NOX sensor could result in easier tampering. We are
continuing to consider these issues and comments. We may consider such
a provision in an appropriate future action. Our final inducement
regulations will reduce the risk of false inducements and provide
increased certainty during repairs by limiting inducements to well-
defined fault conditions that focus appropriately on DEF supply, DEF
quality, and tampering (open-circuit faults associated with missing
aftertreatment hardware).
    We have also learned from the last several years that it is
important to monitor in-use experiences to evaluate whether the
inducement provisions are striking the intended balance of ensuring an
adequate supply of high-quality DEF in a way that is allowing for safe
and timely resolution, even for cases involving difficult
circumstances. For example, we might hypothetically learn from in-use
experiences that component malfunctions, part shortages, or other
circumstances are leaving operators in a place where inducements
prevent them from operating and they are unable to perform maintenance
that is needed to resolve the fault condition. Conversely, we might
hypothetically learn that operators are routinely driving vehicles with
active derates. Information from those in-use experiences may be
helpful for future assessments of whether we should pursue adjustments
to the derate schedules or other inducement provisions we are adopting
in this final rule.
6. In-Use Retrofits To Update Existing Inducement Algorithms
    In the NPRM, we sought comment on whether it would be appropriate
to allow engine manufacturers to modify earlier model year engines to
align with the new regulatory specifications. We did not propose
changes to existing regulations to address this concern. Specifically,
we sought comment on whether and how manufacturers might use field-fix
practices under EPA's field fix guidance to modify in-use engines with
algorithms that incorporate some or all the inducement provisions in
the final rule. We received numerous comments on the need to modify
existing inducement speeds and schedules from operator groups and at
least one manufacturer.\369\ We received comment on the use of field-
fixes for this purpose from CARB, stating that CARB staff does not
support the SCR inducement strategy proposed by EPA and does not
support allowing field fixes for in-use vehicles or to amend the
certification application of current model year engines for the NPRM
inducement strategy. CARB staff also commented that they would support
allowing field fixes for in-use vehicles or amending current
certification applications only if EPA adopts an inducement strategy
identical or similar to the one CARB proposed in their comments on the
proposed rule.\370\ For example, CARB suggested an inducement strategy
with a 5 mph inducement after 10 hours, following an engine restart.
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    \369\ See, for example, comments from the National Association
of Small Trucking Companies, EPA-HQ-OAR-2019-0055-1130.
    \370\ See comments from California Air Resources Board, EPA-HQ-
OAR-2019-0055-1186.
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    EPA believes field fixes with updated inducement algorithms may
fall within EPA's field fix guidance for engines that have EPA-only
certification (i.e., does not include certification to California
standards), but has concerns about such field fixes falling within the
scope of the guidance for engines also certified by CARB if CARB
considers such changes to be tampering with respect to requirements
that apply in California. EPA intends to also consider alternative
field fix inducement approaches that manufacturers choose to develop
and propose to CARB and EPA, for engines certified by both EPA and
CARB, such as approaches that provide a more balanced inducement
strategy than that used in current certifications while still being
effective.

E. Fuel Quality

    EPA has long recognized the importance of fuel quality on motor
vehicle emissions and has regulated fuel quality to enable compliance
with emission standards. In 1993, EPA limited diesel sulfur content to
a maximum of 500 ppm and put into place a minimum cetane index of 40.
Starting in 2006 with the establishment of more stringent heavy-duty
highway PM, NOX and hydrocarbon emission standards, EPA
phased-in a 15-ppm maximum diesel fuel sulfur standard to enable heavy-
duty diesel engine compliance with the more stringent emission
standards.\371\
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    \371\ 66 FR 5002 January 18, 2001.
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    EPA continues to recognize the importance of fuel quality on heavy-
duty vehicle emissions and is not currently aware of any additional
diesel fuel quality requirements necessary for controlling criteria
pollutant emissions from these vehicles.
1. Biodiesel Fuel Quality
    As discussed in Chapter 2.3.2 of the RIA, metals (e.g., Na, K, Ca,
Mg) can enter the biodiesel production stream and can adversely affect
emission control system performance if not sufficiently removed during
production. Our review of data collected by NREL, EPA, and CARB
indicates that biodiesel is compliant with the ASTM D6751-18 limits for
Na, K, Ca, and Mg. As we explained in the proposed rule, the available
data does not indicate that there is widespread off specification
biodiesel blend stock or biodiesel blends in the marketplace. We did
not propose and are not including at this time in this final rule
requirements for biodiesel blend metal content.
    While occasionally there are biodiesel blends with elevated levels
of these metals, they are the exception. Data in the literature
indicates that Na, K, Ca, and Mg levels in these fuels are less than
100 ppb on average. Data further suggests that the low levels measured
in today's fuels are not enough to adversely affect emission control
system performance when the engine manufacturer properly sizes the
catalyst to account for low-level exposure.
    Given the low levels measured in today's fuels, however, we are
aware that ASTM is currently evaluating a possible revision to the
measurement method for Na, K, Ca, and Mg in D6751-20a from EN14538 to a
method that has lower detection limits (e.g., ASTM D7111-16, or a
method based on the ICP-MS method used in the 2016 NREL study). We
anticipate that ASTM will likely specify Na, K, Ca, and Mg limits in a
future update to ASTM 7467-19 for B6 to B20 blends that is an
extrapolation of the B100 limits (see RIA Chapter 2.3.2 for additional
discussion of ASTM test methods, as well as available data on levels of
metal in biodiesel and potential impacts on emission control systems).

2. Compliance Issues Related to Biodiesel Fuel Quality
    Given the concerns we raised in the ANPR and NPRM regarding the
possibility of catalyst poisoning from metals contained in biodiesel
blends and specifically heavy-duty vehicles fueled on biodiesel blends,
and after consideration of comments on the NPRM, EPA is finalizing a
process where we will consider the possibility that an engine was not
properly maintained under the provisions of 40 CFR part 1068, subpart
F, if an engine manufacturer demonstrates that the vehicle was
misfueled in a way that exposed the engine and its aftertreatment
components to metal contaminants and that misfueling degraded the
emission control system performance. This allows a manufacturer to
receive EPA approval to exempt test results from being considered for
potential recall. For example, a manufacturer might request EPA
approval through this process for a vehicle that was historically
fueled on biodiesel blends whose B100 blend stock did not meet the ASTM
D6751-20a limit for Na, K, Ca, and/or Mg (metals which are a byproduct
of current biodiesel production methods). This process requires the
engine manufacturer to provide proof of historic misfueling with off-
specification fuels; more specifically, to qualify for the test result
exemption(s), a manufacturer must provide documentation that compares
the degraded system to a representative compliant system of similar
miles with respect to the content and amount of the contaminant. We are
also finalizing a change from the proposal in the fuel requirements
relevant to conducting in-use testing and to recruitment of vehicles
for in-use testing. The new provision in 40 CFR 1036.415(c)(1) states
that the person conducting the in-use testing may use any commercially
available biodiesel fuel blend that meets the specifications for ASTM
D975 or ASTM D7467 that is either expressly allowed or not otherwise
indicated as an unacceptable fuel in the vehicle's owner or operator
manual or in the engine manufacturer's published fuel recommendations.
As specified in final 40 CFR 1036.410, if the engine manufacturer finds
that the engine was fueled with fuel not meeting the specifications in
40 CFR 1036.415(c)(1), they may disqualify the vehicle from in-use
testing and replace it with another one.

F. Durability Testing

    In this section, we describe the final deterioration factor (DF)
provisions for heavy-duty highway engines, including migration and
updates from their current location in 40 CFR 86.004-26(c) and (d) and
86.004-28(c) and (d) to 40 CFR 1036.245 and 1036.246. EPA regulations
require that a heavy-duty engine manufacturer's application for
certification include a demonstration that the engines will meet
applicable emission standards throughout their regulatory useful life.
This is often called the durability demonstration. Manufacturers
typically complete this demonstration by following regulatory
procedures to calculate a DF. Deterioration factors are additive or
multiplicative adjustments applied to the results from manufacturer
testing to quantify the emissions deterioration over useful life.\372\
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    \372\ See 40 CFR 1036.240(c) and the definition of
``deterioration factor'' in 40 CFR 1036.801, which, as proposed, are
migrated and updated from 40 CFR 86.004-26 and 86.004-28 in this
final rule.
---------------------------------------------------------------------------

    Currently, a DF is determined directly by aging an engine and
exhaust aftertreatment system to useful life on an engine dynamometer.
This time-consuming service accumulation process requires manufacturers
to commit to product configurations well ahead of their pre-production
certification testing to complete the durability testing so EPA can
review the test results before issuing the certificate of conformity.
Some manufacturers run multiple, staggered durability tests in parallel
in case a component failure occurs that may require a complete restart
of the aging process.\373\
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    \373\ See 40 CFR 1065.415.
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    As explained in the NPRM, EPA recognizes that durability testing
over a regulatory useful life is a significant undertaking, which can
involve more than a full year of continuous engine operation for Heavy
HDE to test to the equivalent of the current useful life of 435,000
miles. Manufacturers have been approved, on a case-by-case basis, to
age their systems to between 35 and 50 percent of the current full
useful life on an engine dynamometer, and then extrapolate the test
results to full useful life.\374\ This extrapolation reduces the time
to complete the aging process, but data from a test program shared with
EPA show that while engine out emissions for SCR-equipped engines were
predictable and consistent, actual tailpipe emission levels were higher
by the end of useful life when compared to emission levels extrapolated
to useful life from service accumulation of 75 or lower percent useful
life.375 376 In response to the new data indicating DFs
generated by manufacturers using service accumulation less than useful
life may not be fully representative of useful life deterioration, EPA
initially worked with manufacturers and CARB to address this concern
through guidance for MY 2020 and later engines.
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    \374\ See 40 CFR 86.004-26.
    \375\ U.S. EPA. ``Guidance on Deterioration Factor Validation
Methods for Heavy-Duty Diesel Highway Engines and Nonroad Diesel
Engines equipped with SCR.'' CD-2020-19 (HD Highway and Nonroad).
November 17, 2020.
    \376\ Truck and Engine Manufacturers Association. ``EMA DF Test
Program.'' August 1, 2017.
---------------------------------------------------------------------------

    While the current DF guidance is specific to SCR-equipped engines,
in this final rule we are updating our DF provisions to apply certain
aspects of the current DF guidance to all engine families starting in
model year 2027.\377\ We also are finalizing as proposed that
manufacturers may optionally use these provisions to determine their
deterioration factors for earlier model years. As noted in the
following section, as proposed, we are continuing the option for Spark-
ignition HDE manufacturers to request approval of an accelerated aging
DF determination, as is allowed in our current regulations (see 40 CFR
86.004-26(c)(2)), and our final provision extends this option to all
primary intended service classes. We are not finalizing any changes to
the existing compliance demonstration provision in 40 CFR 1037.103(c)
for evaporative and refueling emission standards. As introduced in
Section III.E, in this rule we are also promulgating refueling emission
standards for incomplete vehicles above 14,000 lb GVWR. As proposed, we
are finalizing that incomplete vehicle manufacturers certifying to the
refueling emission standards for the first time have the option to use
engineering analyses to demonstrate durability using the same
procedures that apply for the evaporative systems on their vehicles
today.
---------------------------------------------------------------------------

    \377\ As noted in Section III.A, the final update to the
definition of ``engine configuration'' in 40 CFR 1036.801, as
proposed, clarifies that hybrid engines and powertrains are part of
a certified configuration and subject to all of the criteria
pollutant emission standards and other requirements; thus the DF
provisions for heavy-duty engines discussed in this subsection will
apply to configurations that include hybrid components.
---------------------------------------------------------------------------

    In Section IV.F.1, we are finalizing two methods for determining
DFs in a new 40 CFR 1036.245 with some modifications from those
proposed, including a new option to bench-age the aftertreatment system
to limit the burden of generating a DF over the lengthened useful life
periods in Section IV.A.3. We are also codifying two DF verification
options available to

manufacturers in the recent DF guidance, with some modifications from
our proposed DF verification requirements. As described in Section
IV.F.2, under the final 40 CFR 1036.245 and 40 CFR 1036.246, the final
provisions include two options for DF verification to confirm the
accuracy of the DF values submitted by manufacturers for certification,
and will be required upon request from EPA. In Section IV.F.3, we
introduce a test program to evaluate a rapid-aging protocol for diesel
catalysts, the results of which we used to develop a rapid-aging test
procedure for CI engine manufacturers to be able to use in their
durability demonstration under 40 CFR 1036.245(c)(6). We are finalizing
this procedure in 40 CFR part 1065, subpart L, as new sections 40 CFR
1065.1131 through 40 CFR 1065.1145.
    At this time we are not finalizing any additional testing
requirements for manufacturers to demonstrate durability of other key
components included in a hybrid configuration (e.g., battery durability
testing). We will consider additional requirements in a future rule as
we pursue other durability-related provisions for EVs, PHEVs, etc.
    As described in Section XI.A.8, we are also finalizing as proposed
that manufacturers of nonroad engines may use the procedures described
in this section to establish deterioration factors based on bench-aged
aftertreatment, along with any EPA-requested in-use verification
testing.
1. Options for Determining Deterioration Factor
    Accurate methods to demonstrate emission durability are key to
ensuring certified emission levels represent real world emissions, and
the efficiency of those methods is especially important in light of the
lengthening of useful life periods in this final rule. To address these
needs, we are migrating our existing regulatory option from part 86 to
part 1036 and including a new option for heavy-duty highway engine
manufacturers to determine DFs for certification. We note that
manufacturers apply these deterioration factors to determine whether
their engines meet the duty cycle standards.
    Consistent with existing regulations, final 40 CFR 1036.245 allows
manufacturers to continue the current practice of determining DFs based
on engine dynamometer-based aging of the complete engine and
aftertreatment system out to regulatory useful life. In addition, under
the new DF determination option, which includes some modifications from
that proposed and which are described in this section, manufacturers
perform dynamometer testing of an engine and aftertreatment system to a
minimum required mileage that is less than regulatory useful life.
Manufacturers then bench age the aftertreatment system to regulatory
useful life and combine the aftertreatment system with an engine that
represents the engine family. Manufacturers run the combined engine and
bench-aged aftertreatment for at least 100 hours before collecting
emission data for determination of the deterioration factor. Under this
option, the manufacturer can use the accelerated bench-aging of diesel
aftertreatment procedure described in Section IV.F.3 that is codified
in the new sections 40 CFR 1065.1131 through 40 CFR 1065.1145 or
propose an equivalent bench-aging procedure and obtain prior approval
from the Agency. For example, a manufacturer might propose a different,
established bench-aging procedure for other engines or vehicles (e.g.,
procedures that apply for light-duty vehicles under 40 CFR part 86,
subpart S).
    We requested comment on whether the new bench-aged aftertreatment
option accurately evaluates the durability of the emission-related
components in a certified configuration, including the allowance for
manufacturers to define and seek approval for a less-than-useful life
mileage for the dynamometer portion of the bench-aging option. This
request for comment specifically included whether or not there is a
need to define a minimum number of engine hours of dynamometer testing
beyond what is required to stabilize the engine before bench-aging the
aftertreatment, noting that EPA's bench-aging proposal focused on
deterioration of emission control components.\378\ We requested comment
on including a more comprehensive durability demonstration of the whole
engine, such as the recent diesel test procedures from CARB's Omnibus
regulation that includes dynamometer-based service accumulation of
2,100 hours or more based on engine class and other factors.\379\ We
also requested comment on whether EPA should prescribe a standardized
aging cycle for the dynamometer portion, as was done by CARB in the
Omnibus rule with their Service Accumulation Cycles 1 and 2.\380\ We
also requested cost and time data corresponding to the current DF
procedures, and projections of cost and time for the proposed new DF
options at the proposed new useful life mileages.
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    \378\ We are updating, as proposed, the definition of ``low-
hour'' in 40 CFR 1036.801 to include 300 hours of operation for
engines with NOX aftertreatment to be considered
stabilized.
    \379\ California Air Resources Board, '' Appendix B-1 Proposed
30-Day Modifications to the Diesel Test Procedures'', May 5, 2021,
Available online: https://ww2.arb.ca.gov/sites/default/files/barcu/regact/2020/hdomnibuslownox/30dayappb1.pdf, page 54.
    \380\ California Air Resources Board, ``Staff Report: Initial
Statement of Reasons for Proposed Rulemaking, Public Hearing to
Consider the Proposed Heavy-duty Engine and Vehicle Omnibus
Regulation and Associated Amendments,'' June 23, 2020. Available
online: https://ww3.arb.ca.gov/regact/2020/hdomnibuslownox/isor.pdf,
page III-80.
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    Some commentors supported the removal of the fuel-based accelerated
DF determination method, noting that it has been shown to underestimate
emission control system deterioration. Other commentors requested that
EPA retain the option, noting that it has been historically allowed.
Fuel-based accelerated aging accelerates the service accumulation using
higher-load operation based on equivalent total fuel flow on a
dynamometer. The engine is only operated out to around 35 percent of UL
based on operating hours, however the high-load operation is intended
to result in an equivalent aging out to full UL. EPA has assessed data
from the EMA DF test program and determined that the data indicated
that the aging mechanism of accelerating the aging at higher load
differs from the actual in-use deterioration
mechanism.381 382 We are not including this option in the
final provisions for determining DF based on our assessment of the
available data and have removed the option in final 40 CFR 1036.245.
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    \381\ U.S. EPA. ``Guidance on Deterioration Factor Validation
Methods for Heavy-Duty Diesel Highway Engines and Nonroad Diesel
Engines equipped with SCR.'' CD-2020-19 (HD Highway and Nonroad).
November 17, 2020.
    \382\ Truck and Engine Manufacturers Association. ``EMA DF Test
Program.'' August 1, 2017.
---------------------------------------------------------------------------

    We also received general support of the use of accelerated aging
cycles to manage the total cost and duration of the DF test, in
addition to some commenters stating that the CARB DF determination
procedure in the CARB Omnibus regulation is superior to the accelerated
aging procedure EPA proposed in 40 CFR 1036.245(b)(2). The required
hours of engine dynamometer aging in the CARB Omnibus procedure
(roughly out to 20 percent of UL for a HHD engine) provide limited
assurance on the performance of engine components out to UL, and thus
primarily provide a short-term quality assurance durability program for
engine hardware. While the purpose of EPA's DF determination procedure
is to

determine emission performance degradation over the useful life of the
engine, we acknowledge that there is value in performing some engine
dynamometer aging. We are finalizing an option to use accelerated
reactor bench-aging of the emission control system that is ten times a
dynamometer or field test (1,000 hours of accelerated aging would be
equivalent to 10,000 hours of standard aging), requiring a minimum
number of testing hours on an engine dynamometer, with the allowance
for the manufacturer to add additional hours of engine dynamometer-
aging at their discretion. The minimum required hours are by primary
intended service class and follow: 300 hours for SI, 1,250 hours for
Light HDE, and 1,500 hours for Medium HDE and Heavy HDE. This option
allows the DF determination to be completed within a maximum of 180
days for a Heavy HDE. We recognize that a different approach, that uses
the same aging duty-cycle for all manufacturers, would provide more
consistency across engine manufacturers. However, no data was provided
by commentors showing that the Service Accumulation Cycles 1 and 2 in
the CARB Omnibus rule are any more effective at determining
deterioration than cycles developed by the manufacturer and submitted
to EPA for approval. EPA is also concerned regarding the amount of idle
contained in each of the CARB Omnibus rule cycles. We realize that this
idle operation was included to target the degradation mechanism that
plagued the SAPO-34 SCR formulations used by manufacturers in the
2010s, however the catalyst developers are aware of this issue now and
have developed formulations that are free from this degradation
mechanism. The two most predominant degradation mechanisms are time at
high temperature and sulfur exposure, including the effects of catalyst
desulfation, and as such EPA favors duty-cycles with more aggressive
aftertreatment temperature profiles. We understand that catalyst
manufacturers now bench test the catalyst formulations under the
conditions that led to the SAPO-34 degradation to ensure that this
degradation mechanism is not present in newly developed SCR
formulations. After taking all of the comments received into
consideration, EPA has added two specified duty-cycle options in 40 CFR
1036.245(c) for DF determination, that are identical to CARB's Service
Accumulation Cycles 1 and 2. Cycle 1 consists of a combination of FTP,
RMC, LLC and extended idle, while Cycle 2 consists of a combination of
HDTT, 55-cruise, 65-cruise, LLC, and extended idle. In the case of the
second option, the manufacturer is required to use good engineering
judgment to choose the vehicle subcategory and vehicle configuration
that yields the highest load factor using the GEM model. EPA is also
providing an option for manufacturers to use their own duty cycles for
DF determination subject to EPA approval and we expect a manufacturer
to include light-load operation if it is deemed to contribute to
degradation of the aftertreatment performance. We also note that we are
finalizing requirements to stop, cooldown, and restart the engine
during service accumulation when using the options that correspond to
CARB Service Accumulation Cycles 1 and 2 for harmonization purposes,
however we note that manufacturers may make a request to EPA to remove
this requirement on a case-by-case basis.
    We are finalizing critical emission-related maintenance as
described in 40 CFR 1036.125(a)(2) and 1036.245(c) in this final rule.
Under this final rule, manufacturers may make requests to EPA for
approval for additional emission-related maintenance actions beyond
what is listed in 40 CFR 1036.125(a)(2), as described in 40 CFR
1036.125(a)(1) and as allowed during deterioration testing under 40 CFR
1036.245(c).
2. Options for Verifying Deterioration Factors
    We are finalizing, with some modifications from proposal, a new 40
CFR 1036.246 where, at EPA's request, the manufacturers would be
required to verify an engine family's deterioration factor for each
duty cycle up to 85 percent of useful life. Because the manufacturer
must comply with emission standards out to useful life, we retain the
authority to verify DF. We proposed requiring upfront verification for
all engine families, but have decided to make this required only in the
event that EPA requests verification. We intend to make such a request
primarily when EPA becomes aware of information suggesting that there
is an issue with the DF generated by the manufacturer. EPA anticipates
that a DF verification request may be appropriate due to consideration
of, for example: (1) Information indicating that a substantial number
of in-use engines tested under subpart E of this part failed to meet
emission standards, (2) information from any other test program or any
other technical information indicating that engines will not meet
emission standards throughout the useful life, (3) a filed defect
report relating to the engine family, (4) a change in the technical
specifications for any critical emission-related components, and (5)
the addition of a new or modified engine configuration such that the
test data from the original emission-data engine do not clearly
continue to serve as worst-case testing for certification. We are
finalizing as proposed that manufacturers may request use of an
approved DF on future model year engines for that engine family, using
the final updates to carryover engine data provisions in 40 CFR
1036.235(d), with the final provision clarifying that we may request DF
verification for the production year of that new model year as
specified in the new 40 CFR 1036.246. As also further discussed in the
following paragraphs, we are not finalizing at this time certain DF
verification provisions that we had proposed regarding timing of when
EPA may request DF verification and certain provisions for the first
model year after a failed result. Our revisions from proposal
appropriately provide flexibility for EPA to gather information based
on DF concerns. The final provisions specify that we will discuss with
the manufacturer the selection criteria for vehicles with respect to
the target vehicle mileage(s) and production model year(s) that we want
the manufacturer to test. We are finalizing that we will not require
the manufacturer to select vehicles whose mileage or age exceeds 10
years or 85 percent of useful life.
    We originally included three testing options in our proposed DF
verification provisions. We are finalizing two of these options and we
are not including the option to verify DF by measuring NOX
emissions using the vehicle's on-board NOX measurement
system at this time. For the two options we are finalizing,
manufacturers select in-use engines meeting the criteria in 40 CFR
1036.246(a), including the appropriate mileage specified by EPA
corresponding to the production year of the engine family.
    Under the first verification option in 40 CFR 1036.246(b)(1),
manufacturers test at least two in-use engines over all duty cycles
with brake-specific emission standards in 40 CFR 1036.104(a) by
removing each engine from the vehicle to install it on an engine
dynamometer and measure emissions. Manufacturers determine compliance
with the emission standards after applying infrequent regeneration
adjustment factors to their measured results, just as they did when
they originally certified the engine family. We are also finalizing a
requirement under this option to allow EPA to request that
manufacturers

perform a new determination of infrequent regeneration adjustment
factors to apply to the emissions from the engine dynamometer-based
testing. Consistent with the proposal, the engine family passes the DF
verification if 70 percent or more of the engines tested meet the duty-
cycle emission standards in 40 CFR 1036.104(a), including any
associated compliance allowance, for each pollutant over all duty
cycles. If a manufacturer chooses to test two engines under this
option, both engines have to meet the standards. Under this option, the
aftertreatment system, including all the associated wiring, sensors,
and related hardware or software is installed on the test engine. We
are finalizing an allowance in 40 CFR 1036.246(a) for the manufacturer
to use hardware or software in testing that differs from those used for
engine family and power rating with EPA approval.
    Under the second verification option in 40 CFR 1036.246(b)(2), as
proposed, manufacturers test at least five in-use engines, to account
for the increased variability of vehicle-level measurement, while
installed in the vehicle using a PEMS. Manufacturers bin and report the
emissions following the in-use testing provisions in 40 CFR part 1036,
subpart E. Compliance is determined by comparing emission results to
the off-cycle emission standards in 40 CFR 1036.104(a) with any
associated compliance allowance, mean ambient temperature adjustment,
and, accuracy margin for each pollutant for each bin after adjusting
for infrequent regeneration.\383\ As proposed, the engine family passes
the DF verification if 70 percent or more of the engines tested meet
the off-cycle standards for each pollutant for each bin. In the event
that EPA requested DF verification and a DF verification fails under
the PEMS option, consistent with the proposal the manufacturer can
reverse a fail determination for the PEMS-based testing and verify the
DF using the engine dynamometer testing option in 40 CFR
1036.246(b)(1).
---------------------------------------------------------------------------

    \383\ For Spark-ignition HDE, we are not finalizing off-cycle
standards; however, for the in-use DF verification options, a
manufacturer compares the engine's emission results to the duty
cycle standards applying a 1.5 multiplier for model years 2027 and
later.
---------------------------------------------------------------------------

    EPA is not including the third option we proposed, to verify DF
using the vehicle's on-board NOX measurement system (i.e., a
NOX sensor), in the final provisions, as we have concerns
that the technology has not matured enough to make this method viable
for DF verification at this time. We did not receive any comments that
supported the availability of technology to enable accurate on-board
NOX measurement at a level needed to show compliance with
the standard. EPA acknowledges the challenges associated with the
development of a functional onboard NOX measurement method,
including data acquisition and telematic system capabilities, and may
reconsider this option in the future if the technology evolves.
    As noted in the preceding paragraphs, we are not taking final
action at this time on the proposed 40 CFR 1036.246(h) provision that
proposed a process for the first MY after a DF verification resulted in
failure. Instead, we are adopting a process for DF verification
failures similar to the existing process used for manufacturer run in-
use testing failures under 40 CFR part 1036, subpart E, such that a
failure may result in an expanded discovery process that could
eventually lead to recall under our existing provisions in 40 CFR part
1068, subpart F. EPA is making this change from proposal because this
approach provides consistency with and builds upon existing processes.
    The final 40 CFR 1036.246(a) specifies how to select and prepare
engines for testing. Manufacturers may exclude selected engines from
testing if they have not been properly maintained or used and the
engine tested must be in a certified configuration, including its
original aftertreatment components. Manufacturers may test engines that
have undergone critical emission-related maintenance as allowed in 40
CFR 1065.410(d), but may not test an engine if its critical emission-
related components had any other major repair.
3. Accelerated Deterioration Factor Determination
    As discussed in Section IV.F.1, we are finalizing a deterioration
factor procedure where manufacturers use engine dynamometer testing for
the required minimum number of hours given in Table 1 to Paragraph
(c)(2) of 40 CFR 1036.245 in combination with an accelerated
aftertreatment catalyst aging protocol in their demonstration of heavy-
duty diesel engine aftertreatment durability through useful life. EPA
has approved accelerated aging protocols for spark-ignition engine
manufacturers to apply in their durability demonstrations for many
years. Historically, while CI engine manufacturers have the ability to
request EPA approval of an accelerated aging procedure, CI engine
manufacturers have largely opted to seek EPA approval to use a service
accumulation fuel based accelerated test with reduce mileage and
extrapolate to determine their DF.
    Other regulatory agencies have promulgated accelerated aging
protocols,384 385 and we have evaluated how these or similar
protocols apply to our heavy-duty highway engine compliance program.
EPA has validated and is finalizing an accelerated aging procedure in
40 CFR part 1065, subpart L, as new sections 40 CFR 1065.1131 through
40 CFR 1065.1145 that CI engine manufacturers can choose to use in lieu
of developing their own protocol as described in 40 CFR 1036.245. The
test program that validated the diesel aftertreatment rapid-aging
protocol (DARAP) was built on existing accelerated aging protocols
designed for light-duty gasoline vehicles (64 FR 23906, May 4, 1999)
and heavy-duty engines.\386\
---------------------------------------------------------------------------

    \384\ California Air Resources Board. California Evaluation
Procedure For New Aftermarket Diesel Particulate Filters Intended As
Modified Parts For 2007 Through 2009 Model Year On-Road Heavy-Duty
Diesel Engines, March 1, 2017. Available online: https://ww3.arb.ca.gov/regact/2016/aftermarket2016/amprcert.pdf.
    \385\ European Commission. Amending Regulation (EU) No 583/2011,
20 September 2016. Available online: https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:32016R1718&from=HU.
    \386\ Eakle, S and Bartley, G (2014), ``The DAAAC Protocol for
Diesel Aftertreatment System Accelerated Aging''.
---------------------------------------------------------------------------

i. Diesel Aftertreatment Rapid Aging Protocol
    The objective of the DARAP validation program was to artificially
recreate the three primary catalytic deterioration processes observed
in field-aged aftertreatment components: Thermal aging based on time at
high temperature, chemical aging that accounts for poisoning due to
fuel and oil contamination, and deposits. The validation program had
access to three baseline engines that were field-aged to the model year
2026 and earlier useful life of 435,000 miles. Engines and their
corresponding aftertreatment systems were aged using the current,
engine dynamometer-based durability test procedure for comparison of
the results to the accelerated aging procedure. We performed
accelerated aging of the catalyst-based aftertreatment systems using
two different methods with one utilizing a burner \387\ and the other
using an engine as the source of aftertreatment aging conditions. The
validation test plan compared emissions at the following approximate
intervals: 0 percent, 25 percent, 50 percent, 75 percent, and 100
percent of the model year 2026 and earlier useful life of 435,000
miles. At proposal, we included

additional details of our DARAP test program in a memo to the
docket.\388\
---------------------------------------------------------------------------

    \387\ A burner is a computer controlled multi-fuel reactor
designed to simulate engine aging conditions.
    \388\ Memorandum to Docket EPA-HQ-OAR-2019-0055: ``Diesel
Aftertreatment Rapid Aging Program''. George Mitchell. May 5, 2021.
---------------------------------------------------------------------------

    The DARAP validation program has completed testing of two rapidly
aged aftertreatment systems, engine and burner, and two engines, a
single FUL aged engine and a 300-hour aged engine. Our memo to the
docket includes a summary of the validation results from this program.
The results show that both accelerated aging pathways, burner and
engine, produced rapidly aged aftertreatment system results that were
not statistically significant when compared to the 9,800-hour
dynamometer aged reference system. We are currently completing
postmortem testing to evaluate the deposition of chemical poisoning on
the surface of the substrates to see how this compares to the
dynamometer aged reference system. The complete results from our
validation program are contained in a final report in the docket.\389\
---------------------------------------------------------------------------

    \389\ Sharp, C. (2022). Demonstration of Low NOX
Technologies and Assessment of Low NOX Measurements in
Support of EPA's 2027 Heavy Duty Rulemaking. Southwest Research
Institute. Final Report EPA Contract 68HERC20D0014.
---------------------------------------------------------------------------

ii. Diesel Aftertreatment Accelerated Aging Test Procedure
    The final provisions include an option for manufacturers to use the
method from the DARAP test program for DF determination and streamline
approval under 40 CFR 1036.245(c). This accelerated aging method we are
finalizing in 40 CFR part 1065, subpart L, as new sections 40 CFR
1065.1131 through 40 CFR 1065.1145 is a protocol for translating field
data that represents a given application (e.g., engine family) into an
accelerated aging cycle for that given application, as well as methods
for carrying out reactor or engine accelerated aging using that cycle.
While this testing can be carried out on an engine as well as reactor
bench, the engine option should not be confused with standard engine
dynamometer aging out to useful life or the historic fuel-based engine
dynamometer accelerated aging typically done out to 35 percent of
useful life approach that EPA will no longer allow under this final
rule. The engine option in this procedure uses the engine (1) as a
source of accelerated sulfur from the combusted fuel, (2) as a source
for exhaust gas, and (3) to generate heat. The catalyst poisoning
agents (oil and sulfur) as well as the temperature exposure are the
same between the two methods and the DARAP test program data
corroborates this. This protocol is intended to be representative of
field aging, includes exposure to elements of both thermal and chemical
aging, and is designed to achieve an acceleration of aging that is ten
times a dynamometer or field test (1,000 hours of accelerated aging
would be equivalent to 10,000 hours of standard aging).
    The initial step in the method requires the gathering and analysis
of input field data that represent a greater than average exposure to
potential field aging factors. The field aging factors consist of
thermal, oil, and sulfur exposure. The thermal exposure is based on the
average exhaust temperature; however, if the engine family incorporates
a periodic infrequent regeneration event that involves exposure to
higher temperatures than are observed during normal (non-regeneration)
operation, then this temperature is used. Oil exposure is based on
field and laboratory measurements to determine an average rate of oil
consumption in grams per hour that reaches the exhaust. Sulfur exposure
is based on the sum of fuel- and oil-related sulfur consumption rates
for the engine family. The procedure provides details on how to gather
data from field vehicles to support the generation and analysis of the
field data.
    Next, the method requires determination of key components for
aging. Most diesel aftertreatment systems contain multiple catalysts,
each with their own aging characteristics. This accelerated aging
procedure ages the system, not component-by-component. Therefore, it is
necessary to determine which catalyst components are the key components
that will be used for deriving and scaling the aging cycle. This
includes identification of the primary and secondary catalysts in the
aftertreatment system, where the primary is the catalyst that is
directly responsible for most of the NOX reduction, such as
a urea SCR catalyst in a compression-ignition aftertreatment system.
The secondary is the catalyst that is intended to either alter exhaust
characteristics or generate elevated temperature upstream of the
primary catalyst, such as a DOC placed upstream of an SCR catalyst,
with or without a DPF in between.
    The next step in the process is to determine the thermal
deactivation rate constant(s) for each key component. This is used for
the thermal heat load calculation in the accelerated aging protocol.
The calculations for thermal degradation are based on the use of an
Arrhenius rate law function to model cumulative thermal degradation due
to heat exposure. The process of determining the thermal deactivation
rate constant begins with determining what catalyst characteristic will
be tracked as the basis for measuring thermal deactivation. Generally,
ammonia storage is the key aging metric for zeolite-based SCR
catalysts, NOX reduction efficiency at low temperature for
vanadium-based SCR catalysts, conversion rate of NO to NO2
for DOCs with a downstream SCR catalyst, and HC reduction efficiency
(as measured using ethylene) at 200 [deg]C for DOCs where the
aftertreatment system does not contain an SCR catalyst for
NOX reduction. Thermal degradation experiments are then
carried out over at least three different temperatures that accelerate
thermal deactivation such that measurable changes in the aging metric
can be observed at multiple time points over the course of no more than
50 hours. During these experiments it is important to void temperatures
that are too high to prevent rapid catalyst failure by a mechanism that
does not represent normal aging.
    Generation of the accelerated aging cycle for a given application
involves analysis of the field data to determine a set of aging modes
that will represent that field operation. There are two methods of
cycle generation in 40 CFR 1065.1139, each of which is described
separately. Method 1 involves the direct application of field data and
is used when the recorded data includes sufficient exhaust flow and
temperature data to allow for determination of aging conditions
directly from the field data set. Method 2 is meant to be used when
insufficient flow and temperature data is available from the field
data. In Method 2, the field data is used to weight a set of modes
derived from the laboratory certification cycles for a given
application. These weighted modes are then combined with laboratory
recorded flow and temperatures on the certification cycles to derive
aging modes. There are two different cases to consider for aging cycle
generation, depending on whether or not a given aftertreatment system
incorporates the use of a periodic regeneration event. For the purposes
of cycle generation, a regeneration is any event where the operating
temperature of some part of the aftertreatment system is raised beyond
levels that are observed during normal (non-regeneration) operation.
The analysis of regeneration data is considered separately from normal
operating data.
    The process of cycle generation begins with the determination of
the number of bench aging hours. The input into this calculation is the
number of real or field

hours that represent the useful life for the target application. The
target for the accelerated aging protocol is a 10-time acceleration of
the aging process, therefore the total number of aging hours is set at
service accumulation hours minus required engine dynamometer aging
hours divided by 10. The hours will then be among different operating
modes that will be arranged to result in repetitive temperature cycling
over that period. For systems that incorporate periodic regeneration,
the total duration will be split between regeneration and normal (non-
regeneration) operation. The analysis of the operation data develops a
reduced set of aging modes that represent normal operation using either
Method 1 or Method 2. Method 1 is a direct clustering method and
involves three steps: Clustering analysis, mode consolidation, and
cycle building.\390\ This method is used when sufficient exhaust flow
and temperature data are available directly from the field data. Method
2 is a cluster-based weighting of certification cycle modes when there
is insufficient exhaust flow and temperature data from the field at the
time the cycle is being developed. The initial candidate mode
conditions are temperature and flow rate combinations that are the
centroids from the analysis of each cluster.
---------------------------------------------------------------------------

    \390\ https://documentation.sas.com/doc/en/emref/14.3/
n1dm4owbc3ka5jn11yjkod7ov1va.htm#:~:text=The%20cubic%20clustering%20c
riterion%20(CCC,evaluated%20by%20Monte%20Carlo%20methods.
---------------------------------------------------------------------------

    The target for accelerated aging cycle operation is to run all the
regenerations that would be expected over the course of useful life and
the procedure provides a process for determining a representative
regeneration profile that will be used during aging. Heat load
calculation and cycle tuning are performed after the preliminary cycles
have been developed for both normal and regeneration operation. The
target cumulative deactivation is determined from the input field data,
and then a similar calculation is performed for the preliminary aging
cycle. If the cumulative deactivation for the preliminary cycle does
not match cumulative deactivation from the field data, then the cycle
is tuned over a series of steps described in 40 CFR 1065.1139 until the
target is matched.
    The final assembly of the candidate accelerated aging cycle
involves the assembly of the target modes into a schedule of modes laid
out on a time basis that can be repeated until the target number of
aging hours has been reached. For cycles that incorporate periodic
regeneration modes, the regeneration frequency and duration, including
any regeneration extension added to reach thermal targets, will be used
to determine the length of the overall cycle. The number of these
cycles that is run is equal to the total number of regenerations over
full useful life. The duration of each cycle is total number of
accelerated aging hours divided by the total number of regenerations.
For multiple components with differing regeneration schedules, this
calculation is performed using the component with the fewest total
number of regenerations. The regeneration events for the more
frequently regenerating components should be spaced evenly throughout
each cycle to achieve the appropriate regeneration frequency and
duration.
    The regeneration duration (including extension) is then subtracted
from the base cycle duration to calculate the duration of normal (non-
regeneration) operation in seconds. This time is split among the normal
(non-regeneration) modes in proportion to the overall target aging time
in each mode. These modes are then split and arranged to achieve the
maximum thermal cycling between high and low temperatures. No mode may
have a duration shorter than 900 seconds, not including transition
time. Mode transitions must be at least 60 seconds long and must be no
longer than 300 seconds. The transition period is considered complete
when you are within 5 [deg]C of the target temperature for the primary
key component. For modes longer than 1800 seconds, you may count the
transition time as time in mode. For modes shorter than 1800 seconds,
under the procedure you must not count the transition time as time in
mode. Modes are arranged in alternating order starting with the lowest
temperature mode and proceeding to the highest temperature mode,
followed by the next lowest temperature mode, and so forth.
    The final cycle is expressed as a schedule of target temperature,
exhaust flow rate, and NOX. For a burner-based platform with
independent control of these parameters, this cycle can be used
directly. For an engine-based platform, it is necessary to develop a
schedule of speed and load targets that will produce the target exhaust
conditions based on the capabilities of the engine platform.
    The accelerated oil consumption target is calculated at 10 times
the field average oil consumption that was determined from the field
data and/or laboratory measurements. Under the procedure, this oil
consumption rate must be achieved on average over the aging cycle, and
it must at least be performed during all non-regeneration modes. Under
the procedure, the lubricating oil chosen must meet the normal in-use
specifications and it cannot be altered. The oil is introduced by two
pathways, a bulk pathway and a volatile pathway. The bulk pathway
involves introduction of oil in a manner that represents oil passing
the piston rings, and the volatile pathway involves adding small amount
of lubricating oil to the fuel. Under the procedure, the oil introduced
by the volatile pathway must be between 10 percent and 30 percent of
the total accelerated oil consumption.
    Sulfur exposure related to oil is already taken care of via
acceleration of the oil consumption itself. The target cumulative fuel
sulfur exposure is calculated using the field recorded average fuel
rate data and total field hours assuming a 10-ppm fuel sulfur level
(which was determined as the 90th percentile of available fuel survey
data).
    For an engine-based accelerated aging platform where the engine is
used as the exhaust gas source, accelerated fuel sulfur is introduced
by increasing the fuel sulfur level. The cycle average fuel rate over
the final aging cycle is determined once that target modes have been
converted into an engine speed and load schedule. The target aging fuel
sulfur level that results in reaching the target cumulative fuel sulfur
exposure is determined from the field data using the aging cycle
average fuel rate and the total number of accelerated aging hours.
    For a burner-based platform, accelerated fuel sulfur is introduced
directly as gaseous SO2. Under the procedure, the
SO2 must be introduced in a manner that does not impede any
burner combustion, and only in a location that represents the exhaust
conditions entering the aftertreatment system. Under the procedure, the
mass rate of sulfur that must be introduced on a cycle average basis to
reach the target cumulative fuel sulfur exposure from the field data is
determined after the final aging cycle has been generated.
    The accelerated aging protocol is run on a bench aging platform
that includes features necessary to successfully achieve accelerated
aging of thermal and chemical aging factors. This aging bench can be
built around either an engine or a burner as the core heat generating
element. The requirements for both kinds of bench aging platform are
described in the following paragraphs.
    The engine-based accelerated aging platform is built around the use
of a diesel engine for generation of heat and flow. The engine used
does not need to be the same engine as the application that is being
aged. Any diesel engine can be used, and the engine may be

modified as needed to support meeting the aging procedure requirements.
You may use the same bench aging engine for deterioration factor
determination from multiple engine families. The engine must be capable
of reaching the combination of temperature, flow, NOX, and
oil consumption targets required. Using an engine platform larger than
the target application for a given aftertreatment system can provide
more flexibility to achieve the target conditions and oil consumption
rates.
    To increase the range of flexibility of the bench aging engine
platform, the test cell setup should include additional elements to
allow more independent control of exhaust temperature and flow than
would be available from the engine alone. For example, exhaust heat
exchangers and/or the use of cooled and uncooled exhaust pipe can be
useful to provide needed flexibility. When using heat exchangers under
this procedure, you must ensure that you avoid condensation in any part
of the exhaust system prior to the aftertreatment. You can also control
engine parameters and the calibration on the engine to achieve
additional flexibility needed to reach the target exhaust conditions.
    Under this procedure, oil consumption must be increased from normal
levels to reach the target of 10 times oil consumption. As noted
earlier, oil must be introduced through a combination of a bulk
pathway, which represents the majority of oil consumption past the
piston rings, and a volatile pathway, which is achieved by adding small
amounts of lube oil to the fuel. The total oil exposure via the
volatile pathway must be between 10 percent and 30 percent of the total
accelerated oil consumption. Under this procedure, the remainder of the
oil consumption must be introduced via the bulk pathway. The volatile
portion of the oil consumption should be introduced and monitored
continuously via a mass flow meter or controller.
    Under this procedure, the engine will need to be modified to
increase oil consumption via the bulk pathway. This increase is
generally achieved through a combination of engine modifications and
the selection of aging speed/load combinations that will result in
increased oil consumption rates. To achieve this, you may modify the
engine in a fashion that will increase oil consumption in a manner such
that the oil consumption is still generally representative of oil
passing the piston rings into the cylinder. Inversion of the top
compression rings as a method which has been used to increase oil
consumption successfully for the DAAAC aging program at SwRI. A
secondary method that has been used in combination with the primary
method involves the modification of the oil control rings in one or
more cylinders to create small notches or gaps (usually no more than
two per cylinder) in the top portion of the oil control rings that
contact the cylinder liner (care must be taken to avoid compromising
the structural integrity of the ring itself).
    Under this procedure, oil consumption for the engine-based platform
must be tracked at least periodically via a drain and weigh process, to
ensure that the proper amount of oil consumption has been achieved. It
is recommended that the test stand include a constant volume oil system
with a sufficiently large oil reservoir to avoid oil ``top-offs''
between oil change intervals. Under this procedure, periodic oil
changes will be necessary on any engine platform, and it is recommended
that the engine be run for at least 72 hours following an oil change
with engine exhaust not flowing through the aftertreatment system to
stabilize oil consumption behavior before resuming aging. A secondary
method for tracking oil consumption is to use clean DPF weights to
track ash loading, and compare this mass of ash to the amount predicted
using the measured oil consumption mass and the oil ash concentration.
The mass of ash found by DPF weight should fall within a range of 55
percent to 70 percent of the of mass predicted from oil consumption
measurements.
    The engine should also include a means of introducing supplemental
fuel to the exhaust to support regeneration if regeneration events are
part of the aging. This can be done either via post-injection from the
engine or using in-exhaust injection. The method and location of
supplemental fuel introduction should be representative of the approach
used on the target application, but manufacturers may adjust this
methodology as needed on the engine-based aging platform to achieve the
target regeneration temperature conditions.
    The burner-based aging platform is built around a fuel-fired burner
as the primary heat generation mechanism. For the accelerated aging
application under this procedure, the burner must utilize diesel fuel
and it must produce a lean exhaust gas mixture. Under this procedure,
the burner must have the ability to control temperature, exhaust flow
rate, NOX, oxygen, and water to produce a representative
exhaust mixture that meets the accelerated aging cycle targets for the
aftertreatment system to be aged. Under this procedure, the burner must
include a means to monitor these constituents in real time, except in
the case of water where the system's water metering may be verified via
measurements made prior to the start of aging (such as with an FTIR)
and should be checked periodically by the same method. Under this
procedure, the accelerated aging cycle for burner-based aging must also
include representative mode targets for oxygen and water, because these
will not necessarily be met by the burner itself through combustion. As
a result, for this procedure the burner will need features to allow the
addition of water and the displacement of oxygen to reach
representative target levels of both. During non-regeneration modes, it
is recommended that the burner be operated in a manner to generate a
small amount of soot to facilitate proper ash distribution in the DPF
system.
    The burner-based platform requires methods for oil introduction for
both the bulk pathway and the volatile pathway. For the bulk pathway,
manufacturers may implement a method that introduces lubricating oil in
a region of the burner that does not result in complete combustion of
the oil, but at the same time is hot enough to oxidize oil and oil
additives in a manner similar to what occurs when oil enters the
cylinder of an engine past the piston rings. Care must be taken to
ensure the oil is properly atomized and mixed into the post-combustion
burner gases before they have cooled to normal exhaust temperatures, to
insure proper digestion and oxidation of the oil constituents. The
volatile pathway oil is mixed into the burner fuel supply and combusted
in the burner. As noted earlier, under this procedure total oil
exposure via the volatile pathway must be between 10 percent and 30
percent of the total accelerated oil consumption. The consumption of
oil in both pathways should be monitored continuously via mass flow
meters or controllers. A secondary method of tracking oil consumption
is to use clean DPF weights to track ash loading and compare this mass
of ash to the amount predicted using the measured oil consumption mass
and the oil ash concentration. The mass of ash found by DPF weight
should fall within a range of 55 percent to 70 percent of the of mass
predicted from oil consumption measurements. This will also ensure that
injected oil mass is actually done in a representative manner so that
it reaches the aftertreatment system.
    Under this procedure, the burner-based platform will also need a
method to introduce and mix gaseous SO2 to achieve the
accelerated sulfur targets. Under this procedure, the consumption

of SO2 must be monitored continuously via a mass flow meter
or controller. SO2 does not need to be injected during
regeneration modes.
    The burner-based platform should also include a means of
introducing supplemental fuel to the exhaust to support regeneration if
regeneration events are part of the aging. We recommend that the method
and location of supplemental fuel introduction be representative of the
approach used on the target application, but manufacturers may adjust
this methodology as needed on the bench engine platform to achieve the
target regeneration temperature conditions. For example, to simulate
post-injected fuel we recommend to introduce the supplemental fuel into
the post-combustion burner gases to achieve partial oxidation that will
produce more light and partially oxidized hydrocarbons similar to post-
injection.
    There are specific requirements for the implementation, running,
and validation of an accelerated aging cycle developed using the
processes described in this section. Some of these requirements are
common to both engine-based and burner-based platforms, but others are
specific to one platform type or the other.
    We recommended carrying out one or more practice aging cycles to
help tune the cycle and aging platform to meet the cycle requirements.
These runs can be considered part of the de-greening of test parts, or
these can be conducted on a separate aftertreatment.
    The final target cycle is used to calculate a cumulative target
deactivation for key aftertreatment components. Manufacturers must also
generate a cumulative deactivation target line describing the linear
relationship between aging hours and cumulative deactivation. The
temperature of all key components is monitored during the actual aging
test and the actual cumulative deactivation based on actual recorded
temperatures is calculated. The cumulative deactivation must be
maintained to within 3 percent of the target line over the course of
the aging run and if you are exceeding these limits, you must adjust
the aging stand parameters to ensure that you remain within these
limits. Under this procedure, you must stay within these limits for all
primary key components. It should be noted that any adjustments made
may require adjustment of the heat rejection through the system if you
are seeing different behavior than the target cycle suggests based on
the field data. If you are unable to meet this requirement for any
tracked secondary system (for example for a DOC where the SCR is the
primary component), you may instead track the aging metric directly and
show that you are within 3 percent of the target aging metric. Note
that this is more likely to occur when there is a large difference
between the thermal reactivity coefficients of different components.
    Calculate a target line for oil accumulation and sulfur
accumulation showing a linear relationship between aging hours and the
cumulative oil exposure on a mass basis. Under this procedure, you must
stay within 10 percent of this target line for oil
accumulation, and within 5 percent of this target line for
sulfur accumulation. In the case of engine-based bulk oil accumulation
you will only be able to track this based on periodic drain and weigh
measurements. For all other chemical aging components, track exposure
based on the continuous data from the mass flow meters for these
chemical components. If your system includes a DPF, it is recommend
that you implement the secondary tracking of oil consumption using DPF
ash loading measurements as describe earlier.
    For the engine-based platform, it will be necessary under this
procedure to develop a schedule of engine operating modes that achieve
the combined temperature, flow, and oil consumption targets. You may
deviate from target NOX levels as needed to achieve these
other targets, but we recommend that you maintain a NOX
level representative of the target application or higher on a cycle
average basis. Note that the need to operate at modes that can reach
the target oil consumption will leverage the flexibility of the engine
stand, and you may need to iterate on the accelerated oil consumption
modifications to achieve a final target configuration. You may need to
adjust the cycle or modify the oil consumption acceleration to stay
within the 10 percent target. In the even that you find
that actual fuel consumption varies from original assumptions, you may
need to adjust the doped fuel sulfur level periodically to maintain the
sulfur exposure within the 5 percent limit.
    If the application uses DEF, it must be introduced to the exhaust
stream in a manner that represents the target application. You may use
hardware that is not identical to the production hardware but ensure
that hardware produces representative performance. Similarly, you may
use hardware that is not identical to production hardware for fuel
introduction into the exhaust as long you ensure that the performance
is representative.
    Under this procedure, for the burner-based platform, you will be
able to directly implement the temperature, flow, NOX,
sulfur, and oil consumption targets. You will also need to implement
water and O2 targets to reach levels representative of
diesel exhaust. We recommend that you monitor and adjust oil and sulfur
dosing on a continuous basis to stay within targets. You must verify
the performance of the oil exposure system via the secondary tracking
of oil exposure via DPF ash loading and weighing measurements. This
will ensure that your oil introduction system is functioning correctly.
If you use a reductant, such as DEF, for NOX reduction, use
good engineering judgement to introduce DEF in a manner that represents
the target application. You may use hardware that is not identical to
the production hardware but ensure that the hardware produces
representative performance. Similarly, you may use hardware that is not
identical to production hardware for fuel introduction into the exhaust
as long you ensure that the performance is representative.
    The implementation and carrying out of these procedures will enable
acceleration of the deterioration factor determination testing, and
generally allow the determination of the deterioration factor out to
useful life, over 90 days of testing.

G. Averaging, Banking, and Trading

    EPA is finalizing an averaging, banking, and trading (ABT) program
for heavy-duty engines that provides manufacturers with flexibility in
their product planning while encouraging the early introduction of
emissions control technologies and maintaining the expected emissions
reductions from the program. Several core aspects of the ABT program we
are finalizing are consistent with the proposed ABT program, but the
final ABT program includes several updates after consideration of
public comments. In particular, EPA requested comment on and agrees
with commenters that a lower family emission limit (FEL) cap than
proposed is appropriate for the final rule. Further, after
consideration of public comments, EPA is not finalizing at this time
the proposed Early Adoption Incentives program, and in turn we are not
including emissions credit multipliers in the final program. Rather, we
are finalizing an updated version of the proposed transitional credit
program under the ABT program. As described in preamble Section IV.G.7,
the revised transitional credit program that we are finalizing provides
four pathways to generate straight NOX

emissions credits (i.e., no credit multipliers) that are valued based
on the extent to which the engines generating credits comply with the
requirements we are finalizing for MY 2027 and later (e.g., credits
discounted at a rate of 40 percent for engines meeting a lower numeric
standard but none of the other MY 2027 and later requirements) (see
section 12 of the Response to Comments document and preamble Section
IV.G.7 for more details). In addition, we are finalizing a production
volume allowance for MYs 2027 through 2029 that is consistent with the
proposal but different in several key aspects, including that
manufacturers will be required to use NOX emissions credits
to certify heavy heavy-duty engines compliant with MY 2010 requirements
in MYs 2027 through 2029 (see Section IV.G.9 for details). Finally, we
are not finalizing the proposed allowance for manufacturers to generate
NOX emissions credits from heavy-duty zero emissions
vehicles (ZEVs) (see Section IV.G.10).
    Consistent with the proposed ABT program, the final ABT program
will maintain several aspects of the ABT program currently specified in
40 CFR 86.007-15, including:
     Allowing ABT of NOX credits with no expiration
of the ABT program,
     calculating NOX credits based on a single
NOX FEL for an engine family,
     specifying FELs to the same number of decimal places as
the applicable standards, and
     calculating credits based on the work and miles of the FTP
cycle.
    In this Section we briefly describe the proposed ABT program, the
comments received on the proposed ABT program, and EPA's response to
those comments. Subsequent subsections provide additional details on
the restrictions we are finalizing for using emission credits in model
years 2027 and later, such as averaging sets (Section IV.G.2), FEL caps
(Section IV.G.4), and limited credit life (Section IV.G.4). See the
proposed rule preamble (87 FR 17550, March 28, 2022) for additional
discussion on the proposed ABT program and the history of ABT for
heavy-duty engines.
    The proposed ABT program allowed averaging, banking, and trading of
NOX credits generated against applicable heavy-duty engine
NOX standards, while discontinuing a credit program for HC
and PM. We also proposed new provisions to clarify how FELs apply for
additional duty cycles. The proposed program included restrictions to
limit the production of new engines with higher emissions than the
standards; these restrictions included FEL caps, credit life for
credits generated for use in MYs 2027 and later, and the expiration of
currently banked credits. These provisions were included in proposed 40
CFR part 1036, subpart H. and 40 CFR 1036.104(c). In addition, we
proposed interim provisions in 40 CFR 1036.150(a)(1) describing how
manufacturers could generate credits in MY 2024 through 2026 to apply
in MYs 2027 and later. We requested comment on several aspects of the
proposed ABT program that we are updating in the final rule, including
the transitional credit program and level of the FEL cap, which
restrict the use of credits in MY 2027 and later.
    Many commenters provided perspectives on the proposed ABT program.
The majority of commenters supported the proposed ABT program, although
several suggested adjustments for EPA to consider in the final rule. In
contrast, a number of commenters opposed the proposed ABT program and
argued that EPA should eliminate the NOX ABT program in the
final rule. Perspectives from commenters supporting and opposing the
proposed ABT program are briefly summarized in this section with
additional details in section 12 of the Response to Comments document.
    Commenters supporting the ABT program stated that it provides an
important flexibility to manufacturers for product planning during a
transition to more stringent standards. They further stated that a
NOX ABT program would allow manufacturers to continue
offering a complete portfolio of products, while still providing real
NOX emissions reductions. In contrast, commenters opposing
the ABT program argued EPA should eliminate the NOX ABT
program in order to maximize NOX emissions reductions
nationwide, particularly in environmental justice communities and other
areas impacted by freight industry. These commenters stated that the
NOX standards are feasible without the use of credits, and
that eliminating the credit flexibilities of an ABT program would be
most consistent with EPA's legal obligations under the CAA.
    EPA agrees with those commenters who support a well-designed ABT
program as a way to help us meet our emission reduction goals at a
faster pace while providing flexibilities to manufacturers to meet new,
more stringent emission standards. For example, averaging, banking, and
trading can result in emissions reductions by encouraging the
development and use of new and improved emission control technology,
which results in lower emissions. The introduction of new emission
control technologies can occur either in model years prior to the
introduction of new standards, or during periods when there is no
change in emissions standards but manufacturers still find it useful to
generate credits for their overall product planning. In either case,
allowing banking and trading can result in emissions reductions earlier
in time, which leads to greater public health benefits sooner than
would otherwise occur; benefits realized sooner in time are generally
worth more to society than those deferred to a later time.\391\ These
public health benefits are further ensured through the use of
restrictions on how and when credits may be used (e.g., averaging sets,
credit life), which are discussed further in this Section IV.G. For
manufacturers, averaging, banking, and trading provides additional
flexibility in their product planning by providing additional lead time
before all of their engine families must comply with all the new
requirements without the use of credits. For periods when no changes in
emission standards are involved, banking can provide manufacturers
additional flexibility, provide assurance against any unforeseen
emissions-related problems that may arise, and in general provide a
means to encourage the development and introduction of new engine
technology (see 55 FR 30585, July 26, 1990, for additional discussion
on potential benefits of an ABT program).
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    \391\ Consistent with economic theory, we assume that people
generally prefer present to future consumption. We refer to this as
the time value of money, which means money received in the future is
not worth as much as an equal amount received today. This time
preference also applies to emissions reductions that result in the
health benefits that accrue from regulation. People have been
observed to prefer health gains that occur immediately to identical
health gains that occur in the future. Health benefits realized in
the near term are therefore worth more to society than those
deferred to a later time.
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    While EPA also agrees with those commenters stating that the
standards in the final rule are feasible without the use of credits, as
described in Section III of this preamble, given the technology-forcing
nature of the final standards we disagree that providing an optional
compliance pathway through the final rule's ABT program is inconsistent
with requirements under CAA section 202(a)(3)(A).\392\ The final ABT
program appropriately balances flexibilities for manufacturers to
generate NOX

emissions credits with updated final restrictions (e.g., credit life,
averaging sets, and family emissions limit (FEL) caps) that in our
judgement both ensure that available emissions control technologies are
adopted and maintain the emissions reductions expected from the final
standards.\393\ An ABT program is also an important foundation for
targeted incentives to encourage manufacturers to adopt advanced
technology before required compliance dates, which we discuss further
in preamble Section IV.G.7 and Section 12 of the Response to Comments
document.
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    \392\ See NRDC v. Thomas, 805 F. 2d 410, 425 (D.C. Cir. 1986),
which upheld emissions averaging after concluding that ``EPA's
argument that averaging will allow manufacturers more flexibility in
cost allocation while ensuring that a manufacturer's overall fleet
still meets the emissions reduction standards makes sense''.
    \393\ As discussed in Section IV.G.9, we are finalizing an
allowance for manufacturers to continue to produce a small number (5
percent of production volume) of engines that meet the current
standards for a few model years (i.e., through MY 2030). See Section
IV.G.9 for details on our approach and rationale for including this
allowance in the final rule.
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    One commenter opposing EPA's proposed NOX emissions ABT
program provided analyses for EPA to consider in developing the final
rule. EPA has evaluated the three approaches to generating credits in
the commenter's analysis: (1) Engines certified below today's standards
which qualify for the proposed transitional credit program, (2) engines
certified to the CARB Omnibus standards which would quality for the
proposed transitional program or on average achieve a standard below
Federal requirements, and (3) ZEVs. For the first category (the
transitional credit program), we considered several factors when
designing the final transitional credit program that are more fully
described in preamble Section IV.G.7; briefly, the transitional credit
program we are finalizing will discount the credits manufacturers
generated from engines certified to levels below today's standards
unless manufacturers can meet all of the requirements in the final MY
2027 and later standards. This includes meeting standards such as the
final low load cycle (LLC), which requires demonstration of emissions
control in additional engine operations (i.e., low load) compared to
today's test cycles. For the second category in the commenter's
analysis (engines certified to Omnibus standards), we recognize that
our proposed rule preamble may have been unclear regarding how the
existing regulations in part 86 and part 1036 apply for purposes of
participation in the Federal ABT program to engines that are certified
to state standards that are different than the Federal standards. We
proposed to migrate without substantive modification the definition of
``U.S.-directed production'' in 40 CFR 86.004-2 to 40 CFR part 1036.801
for criteria pollutant engine requirements, to match the existing
definition for GHG engine requirements, which excludes engines
certified to state emission standards that are different than the
Federal standards.\394\ The relevant existing NOX ABT credit
program requirements, and the relevant program requirements we are
finalizing as proposed, specify that compliance through ABT does not
allow credit calculations to include engines excluded from the
definition of U.S.-directed production volume.\395\ For the third
category in the commenter's analysis (ZEVs), as discussed in preamble
Section IV.G.10 and section 12 of the Response to Comments document, we
are not finalizing the proposed allowance for manufacturers to generate
NOX credits from ZEVs. For these reasons, EPA believes the
final ABT program will at a minimum maintain the emissions reductions
projected from the final rule, and in fact could result in greater
public health benefits by resulting in emissions reductions earlier in
time than they would occur without banking or trading. Further, if
manufacturers generate NOX emissions credits that they do
not subsequently use (e.g., due to transitioning product lines to
ZEVs), then the early emissions reductions from generating these
credits will result in more emission reductions than our current
estimates reflect. In addition, the final ABT program provides an
important flexibility for manufacturers, which we expect will help to
ensure a smooth transition to the new standards and avoid delayed
emissions reductions due to slower fleet turnover than may occur
without the flexibility of the final ABT program.
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    \394\ See Section XI.B.4 for additional information.
    \395\ See final part 1036, subpart H. Existing 40 CFR
1036.705(c) states the following, which we are finalizing as
proposed as also applicable to NOX ABT: ``As described in
Sec.  1036.730, compliance with the requirements of this subpart is
determined at the end of the model year based on actual U.S.-
directed production volumes. Keep appropriate records to document
these production volumes. Do not include any of the following
engines to calculate emission credits: . . . (4) Any other engines
if we indicate elsewhere in this part 1036 that they are not to be
included in the calculations of this subpart.'' See also existing 40
CFR 86.007-15 (regarding U.S.-directed production engines for the
purpose of using or generating credits during a phase-in of new
standards) and 66 FR 5114, January 18, 2001.
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    In the subsections that follow we briefly summarize and provide
responses to comments on several more specific topics, including: ABT
for pollutants other than NOX (IV.G.1), Applying the ABT
provisions to multiple NOX duty-cycle standards (IV.G.2),
Averaging Sets (IV.G.3), FEL caps (IV.G.4), Credit Life (IV.G.5),
Existing credits (IV.G.6), Transitional Credits (IV.G.7), the proposed
Early Adoption Incentives (IV.G.8), and a Production Volume Allowance
under ABT (IV.G.9). The final ABT program is specified in 40 CFR part
1036, subpart H.\396\ Consistent with the proposal, we are also
finalizing a new paragraph at 40 CFR 1036.104(c) to specify how the ABT
provisions will apply for MY 2027 and later heavy-duty engines subject
to the final criteria pollutant standards in 40 CFR 1036.104(a). The
Transitional Credit program in the final rule is described in the
interim provision in 40 CFR 1036.150(a)(1), which we are finalizing
with revisions from the proposal.
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    \396\ As proposed, the final rule does not include substantive
revisions to the existing GHG provisions in 40 CFR 1036, subpart H;
as proposed, the final revisions clarify whether paragraphs apply
for criteria pollutant standards or GHG standards.
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1. ABT for Pollutants Other Than NOX
    After consideration of public comments, EPA is choosing to finalize
as proposed an ABT program that will not allow averaging, banking, or
trading for HC (including NOX+NMHC) or PM for MY 2027 and
later engines. This includes not allowing HC and PM emissions credits
from prior model years to be used for MY 2027 and later engines. For
engines certified to MY 2027 or later standards, manufacturers must
demonstrate in their application for certification that they meet the