(a) Applicability and general provisions. The criteria exhaust emission standards of this section apply for both light-duty program vehicles and medium-duty vehicles, starting with model year 2027.

(1) A vehicle meeting all the requirements of this section is considered a Tier 4 vehicle meeting the Tier 4 standards. Vehicles meeting some but not all requirements are considered interim Tier 4 vehicles as described in paragraph (b)(6)(iv) of this section.

(2) The Tier 4 standards include testing over a range of driving schedules and ambient temperatures. The standards for 25 °C or 35 °C testing in paragraph (b) of this section apply separate from the −7 °C testing in paragraph (c) of this section. We may identify these standards based on nominal ambient test temperatures. Note that −7 °C testing is also identified as cold temperature testing elsewhere in this subpart.

(3) See § 86.1813 for evaporative and refueling emission standards.

(4) See § 86.1818 for greenhouse gas emission standards.

(b) Exhaust emission standards for 25 and 35 °C testing. Exhaust emissions may not exceed standards over several driving cycles as follows:

(1) Measure emissions using the chassis dynamometer procedures of 40 CFR part 1066, as follows:

(i) Establish appropriate load settings based on loaded vehicle weight for light-duty program vehicles and adjusted loaded vehicle weight for medium-duty vehicles (see § 86.1803).

(ii) Emission standards under this paragraph (b) apply for all the following driving cycles unless otherwise specified:

(iii) Testing occurs at (20-30) °C ambient temperatures, except that a nominal ambient temperature of 35.0 °C applies for testing over the SC03 driving cycle. See paragraph (c) of this section for emission standards and measurement procedures that apply for cold temperature testing.

(iv) Hydrocarbon emission standards are expressed as NMOG; however, for certain vehicles you may measure exhaust emissions based on nonmethane hydrocarbon instead of NMOG as described in 40 CFR 1066.635.

(v) Measure emissions from hybrid electric vehicles (including plug-in hybrid electric vehicles) as described in 40 CFR part 1066, subpart F, except that these procedures do not apply for plug-in hybrid electric vehicles during charge-depleting operation.

(2) Fully phased-in standards apply as specified in the following table:

(3) The FTP standards specified in this paragraph (b) apply equally for testing at low-altitude conditions and high-altitude conditions. The US06, SC03, and HFET standards apply only for testing at low-altitude conditions.

(4) The NMOG+NOX emission standard is based on a fleet average for a given model year.

(i) You must specify a family emission limit (FEL) for each test group based on the FTP emission standard corresponding to each named bin. The FEL serves as the emission standard for the test group with respect to all specified driving cycles. Calculate your fleet average emission level as described in § 86.1860 to show that you meet the specified fleet average standard. For multi-fueled vehicles, calculate fleet average emission levels based only on emission levels for testing with gasoline or diesel fuel. You may generate emission credits for banking and trading, and you may use banked or traded credits as described in § 86.1861 for demonstrating compliance with the fleet average NMOG+NOX emission standard. You comply with the fleet average emission standard for a given model year if you have enough credits to show that your fleet average emission level is at or below the applicable standard.

(ii) Select one of the identified values from table 2 of this section for demonstrating that your fleet average emission level for light-duty program vehicles complies with the fleet average NMOG+NOX emission standard. These FEL values define emission bins that also determine corresponding emission standards for NMOG+NOX emission standards for ACC II driving cycles, as follows:

(iii) You may select one of the identified values from table 2 to paragraph (b)(4)(ii) of this section for demonstrating that your fleet average emission level for medium-duty vehicles complies with the fleet average NMOG+NOX emission standard. The following additional NMOG+NOX bin standards are also available for medium-duty vehicles: 75, 85, 100, 125, 150, and 170 mg/mile. Medium-duty vehicles are not subject to standards based on the ACC II driving cycles specified in paragraphs (b)(1)(ii)(E) through (G) of this section.

(5) Qualifying vehicles are exempt from certain ACC II bin standards as follows:

(i) Vehicles are exempt from the ACC II bin standards for early driveaway if the vehicle prevents engine starting during the first 20 seconds of a cold-start FTP test interval and the vehicle does not use an electrically heated catalyst or other technology to precondition the engine or emission controls such that NMOG+NOX emissions would be higher during the first 505 seconds of the early driveaway driving cycle compared to the first 505 seconds of the conventional FTP driving cycle.

(ii) Vehicles are exempt from the ACC II bin standards for high-power PHEV engine starts if their all-electric range on the cold-start US06 driving cycles is at or above 10 miles for model years 2027 through 2029, and at or above 40 miles for model year 2030 and later.

(6) The Tier 4 standards phase in over several years, as follows:

(i) Light-duty program vehicles. Include all light-duty program vehicles at or below 6,000 pounds GVWR in the calculation to comply with the Tier 4 fleet average NMOG+NOX standard for 25 °C testing in paragraph (b)(2) of this section. You must meet all the other Tier 4 requirements with 20, 40, 60, and 100 percent of your projected nationwide production volumes in model years 2027 through 2030, respectively. A vehicle counts toward meeting the phase-in percentage only if it meets all the requirements of this section. Fleet average NMOG+NOX standards apply as follows for model year 2027 through 2032 light-duty program vehicles:

(ii) Default phase-in for vehicles above 6,000 pounds GVWR. The default approach for phasing in the Tier 4 standards for vehicle above 6,000 pounds GVWR is for all those vehicles to meet the fully phased in Tier 4 standards of this section starting in model year 2030 for light-duty program vehicles and in model year 2031 for medium-duty vehicles. Manufacturers using this default phase-in for medium-duty vehicles may not use credits generated from earlier model years for demonstrating compliance with the Tier 4 NMOG+NOX standards under this paragraph (b).

(iii) Alternative early phase-in for vehicles above 6,000 pounds GVWR. Manufacturers may use the following alternative early phase-in provisions to transition to the Tier 4 exhaust emission standards on an earlier schedule for vehicles above 6,000 pounds GVWR.

(A) If you select the alternative early phase-in for light-duty program vehicles above 6,000 pounds GVWR, you must demonstrate that you meet the phase-in requirements in paragraph (b)(6)(i) of this section based on all your light-duty program vehicles.

(B) If you select the alternative early phase-in for medium-duty vehicles, include all medium-duty vehicles in the calculation to comply with the Tier 4 fleet average NMOG+NOX standard starting in model year 2027. You must meet all the other Tier 4 requirements with 20, 40, 60, 80, and 100 percent of a manufacturer's projected nationwide production volumes in model years 2027 through 2031, respectively. A vehicle counts toward meeting the phase-in percentage only if it meets all the requirements of this section. Medium-duty vehicles complying with the alternative early phase-in are subject to the following fleet average NMOG+NOX standards for model years 2027 through 2033:

(C) If you select the alternative early phase-in but are unable to meet all the requirements that apply in any model year before model year 2030 for light-duty program vehicles and model year 2031 for medium-duty vehicles, you may switch to the default phase-in. Switching to the default phase-in does not affect certification or compliance obligations for model years before you switch to the default phase-in.

(iv) Interim Tier 4 vehicles. Vehicles not meeting all the requirements of this section during the phase-in are considered “interim Tier 4 vehicles”. Interim Tier 4 vehicles are subject to all the requirements of this subpart that apply for Tier 3 vehicles except for the fleet average NMOG+NOX standards in §§ 86.1811-17 and 86.1816-18. Interim Tier 4 vehicles may certify to the 25 °C fleet average NMOG+NOX standard under this section using all available Tier 3 bins under §§ 86.1811-17 and 86.1816-18. Interim Tier 4 vehicles are subject to the whole collection of Tier 3 bin standards, and they are not subject to any of the Tier 4 bin standards specified in this section. Note that manufacturers complying with the default phase-in specified in paragraph (b)(6)(ii) of this section for Interim Tier 4 light-duty program vehicles above 6,000 pounds GVWR will need to meet a Tier 3 fleet average NMOG+NOX standard in model years 2027 through 2029 in addition to the Tier 4 fleet average NMOG+NOX standard for vehicles at or below 6,000 pounds GVWR in those same years. Note that emission credits from those Tier 3 and Tier 4 light-duty program vehicles remain in the same averaging set.

(v) Phase-in for high-power PHEV engine starts. The following bin standards apply for high-power PHEV engine starts in model years 2027 through 2029 instead of the analogous standards specified in paragraph (b)(4)(ii) of this section:

(vi) MDPV. Any vehicle that becomes an MDPV as a result of the revised definition in § 86.1803-01 starting in model 2027 remains subject to the heavy-duty Tier 3 standards in § 86.1816-18 under the default phase-in specified in paragraph (b)(6)(ii) of this section for model years 2027 through 2030.

(vii) Keep records as needed to show that you meet the requirements specified in this paragraph (b) for phasing in standards and for complying with declining fleet average average standards.

(c) Exhaust emission standards for −7 °C testing. Exhaust emissions may not exceed standards for −7 °C testing, as follows:

(1) Measure emissions as described in 40 CFR 1066.801(c)(1) and (6).

(2) The standards apply to gasoline-fueled and diesel-fueled vehicles, except as specified. Multi-fuel, bi-fuel or dual-fuel vehicles must comply with requirements using only gasoline and diesel fuel, as applicable. Testing with other fuels such as electricity or a high-level ethanol-gasoline blend is not required.

(3) The following standards apply equally for light-duty program vehicles and medium-duty vehicles:

(i) Gasoline-fueled vehicles must meet a fleet average NMOG+NOX standard of 300 mg/mile. Calculate fleet average emission levels as described in § 86.1864. There is no NMOG+NOX standard for diesel-fueled vehicles, but manufacturers must measure and report emissions as described in § 86.1829-15(g).

(ii) The PM standard is 0.5 mg/mile.

(iii) The CO standard is 10.0 g/mile.

(4) The CO standard applies at both low-altitude and high-altitude conditions. The NMOG+NOX and PM standards apply only at low-altitude conditions. However, manufacturers must submit an engineering evaluation indicating that common calibration approaches are utilized at high altitudes. Any deviation from low altitude emission control practices must be included in the auxiliary emission control device (AECD) descriptions submitted at certification. Any AECD specific to high altitude must require engineering emission data for EPA evaluation to quantify any emission impact and validity of the AECD.

(5) Phase-in requirements for standards under this paragraph (c) apply as described in paragraphs (b)(6) and (f) of this section.

(d) Special provisions for spark-ignition engines. The following A/C-on specific calibration provisions apply for vehicles with spark-ignition engines:

(1) A/C-on specific calibrations (e.g., air-fuel ratio, spark timing, and exhaust gas recirculation) that differ from A/C-off calibrations may be used for a given set of engine operating conditions (e.g., engine speed, manifold pressure, coolant temperature, air charge temperature, and any other parameters). Such calibrations must not unnecessarily reduce emission control effectiveness during A/C-on operation when the vehicle is operated under conditions that may reasonably be expected during normal operation and use. If emission control effectiveness decreases as a result of such calibrations, the manufacturer must describe in the Application for Certification the circumstances under which this occurs and the reason for using these calibrations.

(2) For AECDs involving commanded enrichment, these AECDs must not operate differently for A/C-on operation than for A/C-off operation. This includes both the sensor inputs for triggering enrichment and the degree of enrichment employed.

(e) Off-cycle emission standards for high-GCWR vehicles. Model year 2031 and later medium-duty vehicles above 22,000 pounds GCWR must meet off-cycle emission standards as follows:

(1) The engine-based off-cycle emission standards in 40 CFR 1036.104(a)(3) apply for vehicles with compression-ignition engines based on measurement procedures with 2-bin moving average windows. Manufacturers may instead meet the following alternative standards for measurement procedures with 3-bin moving average windows:

(2) The following emission standards apply for spark-ignition engines:

(3) In-use testing requirements and measurement procedures apply as described in § 86.1845-04(h).

(f) Small-volume manufacturers. Small-volume manufacturers may use the following phase-in provisions for light-duty program vehicles:

(1) Instead of the 25 °C fleet average NMOG+NOX standards specified in this section, small-volume manufacturers may meet alternate fleet average standards of 51 mg/mile for model year 2027 and 30 mg/mile for model years 2028 through 2031. The 15 mg/mile standard applies starting in model year 2032.

(2) Instead of the phase-in specified in paragraph (b)(6)(i) of this section, small-volume manufacturers may comply with all the requirements of this section other than the NMOG+NOX standards starting in model year 2032.