Advanced Clean Fleets Regulation - Internal Combustion Engine Purchase Requirements
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When can I add ICE vehicles to my California fleet?
High Priority Fleets that comply with the Model Year Schedule must only add ZEVs to the California fleet starting January 1, 2024, and starting January 1, 2025, must remove internal combustion engines from the California fleet by January 1 of the calendar year after their minimum useful life mileage thresholds are exceeded, or January 1 of the calendar year the engine model year is 18 years old, whichever occurs first. Please see the High Priority and Federal Fleets Overview at https://ww2.arb.ca.gov/resources/fact-sheets/advanced-clean-fleets-regulation-high-priority-and-federal-fleets-overview. ICE vehicles can only be added to the California fleet if an exemption to purchase a new ICE vehicle is granted.
State and local government fleets that comply with the ZEV Purchase Schedule from January 1, 2024 until January 1, 2027 must purchase 50 percent ZEVs and the rest can be ICE vehicles. Starting January 1, 2027, all purchases must be ZEVs. Please see the State & Local Government Agency Fleet Requirements Overview at https://ww2.arb.ca.gov/resources/fact-sheets/advanced-clean-fleets-regulation-state-local-government-agency-fleet.
High Priority Fleets and all government fleets can elect to use the ZEV Milestones Option. The ZEV Milestones Option allows for the addition of new and used ICE engines to the California fleet provided the fleet owner complies with the applicable ZEV Milestone as a percentage of the California fleet. Please see the ZEV Milestones Overview at https://ww2.arb.ca.gov/resources/fact-sheets/advanced-clean-fleets-regulation-zev-milestones-option
ICE vehicles can also be added to the California fleet if an exemption to purchase a new ICE vehicle is granted.
What new engines can be purchased in and operated in California?
California Health and Safety Code (HSC) sections 43151 through 43153 prohibit the sale, offer for sale, or introduction into commerce, or acquisition of new, non-California certified engines in California. Per HSC section 43151(a): “A person shall not offer for sale, introduce into commerce, import, deliver, purchase, rent, lease, acquire, or receive a new motor vehicle, new motor vehicle engine, or motor vehicle with a new motor vehicle engine for use, registration, or resale in this state unless the motor vehicle engine or motor vehicle has been certified to applicable California standards.” These provisions apply to vehicles that are rented or leased in California, as highlighted above.
California’s oxides of nitrogen (NOx) emissions standard set by the Heavy-duty Omnibus regulations for new California-certified 2024 through 2026 model year engines is 0.050 g/bhp-hr, whereas the corresponding federal NOx emissions standard for new federally-certified 2024 through 2026 model year engines in other states is 0.20 g/bhp-hr. A new 0.20 g/bhp-hr legacy engine sold in California must therefore offset all of its excess emissions to be compliant with California’s Heavy-duty Omnibus regulation (i.e., conform to all the requirements specified in California Code of Regulations, title 13, section 1956.8(a)(2)(C)3).
A new vehicle means one that has an odometer reading of less than 7,500 miles. HSC section 43156 creates a conclusive presumption that the legal or equitable title to any motor vehicle with an odometer reading of less than 7,500 miles has not been transferred to an ultimate purchaser (i.e., that the vehicle is considered “new” for the purposes of the previously referenced HSC codes). The initial state of registration is not relevant to whether the new vehicle must offset all of its California-certified engine emissions deficits (i.e., offset excess emissions).
Fleet owners that are subject to the ACF regulation must also meet internal combustion engine requirements specified in sections 2015(r) and 2013(s) when adding ICE vehicles to their California fleet.
If I am adding a new ICE vehicle to my fleet, how do I comply with the ACF regulation?
New ICE vehicles that are purchased in California already have engines that meet California certification requirements, so no further action by the fleet owner is needed. Manufacturers that sell ICE vehicles to the ultimate purchaser in California are already required to meet the California Air Resources Board (CARB) certification requirements.
If an out-of-state fleet purchases a new vehicle outside of California, and the vehicle has a 2024 or 2025 model year California certified or 50-state certified engine, it may still be added to their California fleet to comply with the ICE vehicle addition requirements of section 2015(r) or 2013(s) of the ACF regulation as specified in the enforcement discretion letter. In other words, if an out-of-state fleet is allowed to add ICE vehicles to its California fleet per the ACF rule, it may add such vehicles purchased outside California that are powered by 2024 or 2025 MY engines that are California-certified or 50-state certified but whose excess emissions are not offset and still be considered compliant with the ACF rule. It does not mean the fleet owner can add a vehicle powered by a U.S. Environmental Protection Agency (EPA) certified engine only, also referred as a 49-state certified engine, to its California fleet. Starting with the 2026 model year, however, all ICE vehicle additions to the California fleet will need to be powered by engines certified to applicable California-emissions standards and whose excess emissions are fully offset (i.e., that comply with the Heavy-Duty Omnibus regulation).
What engines are California-certified or 50-state certified?
See Table 1 below for what engines are considered California-certified and 50-state certified referenced in the enforcement discretion letter and what 2024 and 2025 model year engines ACF fleets can add to their California fleet when the ACF regulation allows them to add ICE vehicles instead of ZEVs.
Table 1: Engine Certification and ACF Compliance Status
| Certification Status | California Certified | 50-State Certified | EPA Certified Only (49 State Certified) |
| Engine Family is Certified by | CARB Only | Both CARB and EPA | EPA Only |
| Can 2024 and 2025 model year engines be added to ACF California fleet allowed to add ICE vehicles? | In-state purchases: Yes, if legacy engine emissions are offset by manufacturer | Out-of-state purchases: Yes In-state purchases: Yes, if legacy engine emissions are offset by manufacturer | No |
| Where engines can be sold | In California and S177 States | Nationwide | Outside California and outside S177 States |
| Engine with California Clean Idle Label and Step 1 Warranty | Applicable | Applicable | Not applicable |
| Offsetting of emissions under the CA-ABT program for 2024-2025 model years | Emissions offsetting required if sold as new engine in California. For S177 states, please discuss with the program director in the applicable state. | Emissions offsetting required if sold as new engine in California. For S177 states, please discuss with the program director in the applicable state. | Not applicable |
Acronyms:
S177 States: Refers to states that have adopted the Omnibus regulation under Section 177 of the Clean Air Act
"Step 1 Warranty”: Refers to step 1 warranty requirements described in https://ww2.arb.ca.gov/rulemaking/2018/hd-warranty-2018
CA-ABT: California Heavy-Duty Omnibus Averaging, Banking and Trading program under Title 13, California Code of Regulations, Section 1956.8.
This document is provided to assist regulated entities in complying with the Advanced Clean Fleets regulation. In the event any discrepancy exists between this document and the Advanced Clean Fleets regulation, the regulatory text of the Advanced Clean Fleets regulation applies.