California Air Resources Board (CARB) emission rules still govern most vehicles, fleets, and gas-powered equipment used in the state, even after Congress rolled back several of CARB’s most ambitious zero-emission sales mandates in June 2025. Smog checks, heavy-duty truck requirements, inspection and reporting programs, and the small off-road engine ban all remain fully enforceable, and violations can trigger civil penalties of up to $37,500 per violation along with DMV registration holds.
What the 2025 Federal Preemption Changed
In June 2025, the President signed joint resolutions under the Congressional Review Act preempting three CARB programs: Advanced Clean Cars II (which would have required 100% zero-emission new passenger vehicle sales by the 2035 model year), Advanced Clean Trucks (manufacturer sales mandates for zero-emission trucks), and the Omnibus Low NOx rule. The resolutions declare these programs “fully and expressly preempted by the Clean Air Act” and bar the EPA from granting any future waivers that are “substantially the same.”1The White House. Statement by the President
Everything else stayed in place. Rules that govern in-use vehicles rather than new-vehicle sales, and rules that don’t rely on a Section 209 waiver, continue to apply. If you drive a passenger car, run a trucking fleet, operate landscaping equipment, or manage a public agency fleet, your day-to-day compliance obligations are largely unchanged.
Passenger Vehicle Rules
California’s smog check program is unaffected by the preemption. A smog inspection is required every other year when you renew your vehicle registration, with an exemption for vehicles less than eight model years old. The requirement applies in most populated counties, and your DMV renewal notice tells you whether a smog certification is needed.2Bureau of Automotive Repair. Smog Check: When You Need One and What’s Required3California Department of Motor Vehicles. Smog Inspections
Bringing a vehicle in from another state can be a trap. A vehicle with fewer than 7,500 miles on the odometer that was not originally certified to California emission standards cannot be registered to a California resident, even if it passes a tailpipe test locally. The reading at the time you acquired the vehicle controls whether this restriction applies.4Legal Information Institute. California Code of Regulations Title 13 Section 151.00 – Refusal of Registration
Active-duty military personnel stationed in California can operate vehicles with valid out-of-state plates without registering here. If they choose to register in California, the smog inspection still applies.5California DMV. Vehicle Information for Military Personnel in California
Heavy-Duty Truck and Bus Rules
The Truck and Bus Regulation, in effect since 2008, requires all diesel vehicles over 14,000 pounds operating in California to have a 2010 or newer model year engine and emission system. Because this is an in-use fleet rule rather than a new-vehicle sales mandate, the 2025 preemption does not touch it. Non-compliant vehicles face DMV registration denial.6California Air Resources Board. Truck and Bus Regulation
The Advanced Clean Fleets regulation was originally designed to transition medium- and heavy-duty trucks across many fleet types to zero-emission vehicles. After the federal waiver landscape shifted, CARB withdrew its EPA waiver request but continues to apply the rule to state and local government fleets, which it can regulate without a federal waiver. Those agencies must increase their use of zero-emission vehicles as they replace aging equipment.7California Air Resources Board. Advanced Clean Fleets
Drayage Trucks
Drayage trucks serving seaports and intermodal railyards face stricter deadlines. Since January 1, 2024, any drayage truck newly registering in CARB’s online system must be zero-emission. Legacy trucks already in the system must visit a California seaport or railyard at least once per calendar year to stay registered. By 2035, every drayage truck in the system must be zero-emission.8Legal Information Institute. California Code of Regulations Title 13 Section 2014.1 – In-Use On-Road Heavy-Duty Drayage Trucks Requirements and Compliance Deadlines
Public Transit Buses
Transit agencies follow the Innovative Clean Transit regulation, adopted in 2018. Starting in 2029, every new bus a transit agency purchases must be zero-emission, with full fleet transition targeted for 2040. Because the rule governs public agency purchasing rather than manufacturer sales, it operates independently of the federal waiver process.9California Air Resources Board. Innovative Clean Transit (ICT) Regulation Fact Sheet
Clean Truck Check Inspections
The Clean Truck Check program (also called HD I/M) is California’s testing and compliance system for heavy-duty vehicles. As of March 2026, it is fully in effect for all subject vehicles, including trucks registered in other states that operate within California.10California Air Resources Board. Clean Truck Check Vehicle Inspection System
For 2026, almost all subject vehicles must be tested twice per year. Agricultural vehicles and California-registered motorhomes used for recreation or emergency occupancy need only annual testing. Starting in October 2027, the frequency increases to four times per year for vehicles equipped with on-board diagnostics.11California Air Resources Board. Clean Truck Check – Emissions Compliance Testing Requirements
Owners register through the Clean Truck Check portal and enter each vehicle’s engine family name, VIN, and gross vehicle weight rating. Each vehicle carries an annual compliance fee of $32.13 as of January 1, 2026. Once the system verifies the engine data and processes payment, it issues a compliance certificate that serves as proof during roadside inspections and at weigh stations.12California Air Resources Board. Clean Truck Check Compliance Fee Update Effective 1/1/2026
Small Off-Road Engines
California banned the sale of most new gas-powered small off-road engines starting with the 2024 model year. The ban covers equipment like leaf blowers, lawn mowers, and string trimmers. Retailers cannot stock new gas-powered units in these categories, and manufacturers must offer zero-emission alternatives.13California Air Resources Board. CARB Approves Updated Regulations Requiring Most New Small Off-Road Engines Be Zero Emission
Larger pressure washers follow a different timeline. Their emission standards became 40–90% more stringent in 2024, but the full zero-emission requirement doesn’t take effect until the 2028 model year. Portable generators have their own transition schedule. The rules apply only to newly manufactured equipment. If you already own gas-powered tools, you can keep using them.
Common Exemptions
Trucks that travel fewer than 1,000 miles per year within California can qualify for a low-use exemption from the Truck and Bus Regulation’s engine replacement requirements. Vehicles that operate nationally but log fewer than 1,000 California miles annually also qualify. You must report odometer readings annually through CARB’s TRUCRS system and keep third-party records to prove your mileage if audited.14California Air Resources Board. Truck and Bus Flexibility Options
Authorized emergency vehicles as defined by California Vehicle Code Section 165 are excluded from the Advanced Clean Fleets regulation entirely. Vehicles that aren’t classified as emergency vehicles but are dispatched to support a declared emergency (such as supply transport during a governor-proclaimed disaster) can qualify for a temporary exemption, provided a recognized emergency management agency dispatches them.15California Air Resources Board. Advanced Clean Fleets Regulation – Declared Emergency Response Exemption
Vouchers for Zero-Emission Commercial Vehicles
The Hybrid and Zero-Emission Truck and Bus Voucher Incentive Project (HVIP) offsets the cost of qualifying commercial purchases. Amounts vary by vehicle class:
- Class 3 trucks (10,001–14,000 lbs): $15,000 base voucher, up to $40,000 for small businesses
- Class 6–7 trucks (19,501–33,000 lbs): $85,000 base voucher, up to $160,000 for small businesses
- Class 8 trucks (33,001+ lbs): $120,000 base voucher, up to $330,000 for small businesses
- Class 8 fuel cell trucks: $240,000 base voucher, up to $420,000 for small businesses
Public school buses and transit buses carry even larger incentives, with Class 8 school bus vouchers reaching $216,000 and small public school district vouchers reaching $276,000. Drayage and refuse truck operators receive enhanced voucher amounts above the standard base.16California HVIP. Funding – Clean Truck and Bus Voucher Incentive Project
For passenger vehicles, California’s Clean Vehicle Rebate Project closed in November 2023 with no direct successor. Buyers of electric passenger vehicles may still qualify for federal tax credits under the Inflation Reduction Act, and CARB’s DriveClean tool lists other local and utility incentives.
Penalties and Enforcement
CARB treats emission violations as strict liability. Intent doesn’t matter: if the violation exists, you’re liable regardless of whether you knew about it or tried to prevent it.17California Air Resources Board. Enforcement Policy
Under Health and Safety Code Section 43016, a general violation of CARB rules carries a civil penalty of up to $37,500 per violation. Violations involving small off-road engines or portable fuel containers are capped lower, at $500 per unit.18California Legislative Information. California Health and Safety Code 43016
Administrative penalties assessed under related Health and Safety Code provisions can reach $10,000 per day with a cumulative cap of $100,000, or up to $25,000 per day with a $300,000 cumulative cap for more severe violations. Daily penalties compound quickly, which is where most fleet operators feel the real financial pain.17California Air Resources Board. Enforcement Policy
Beyond fines, CARB can place a registration hold on non-compliant vehicles through the DMV, blocking renewal of your plates. If your vehicle is flagged, the DMV will issue a 90-day temporary operating permit while you bring the vehicle into compliance, but you cannot complete a standard renewal until the hold clears.19California Air Resources Board. DMV Compliance Verification
CARB also has authority under Health and Safety Code Section 43017 to seek court injunctions against ongoing violations, effectively ordering a business to stop operating non-compliant equipment. Businesses that discover violations on their own can use CARB’s voluntary disclosure process to reduce penalties by 25% to 75% depending on the circumstances, and up to 50% of any negotiated penalty can be offset through a Supplemental Environmental Project.17California Air Resources Board. Enforcement Policy