California Diesel Emissions Requirements and Penalties

California’s diesel emissions requirements apply to nearly every heavy-duty vehicle over 14,000 pounds that operates on state roads, no matter where it’s registered. The rules are enforced by the California Air Resources Board (CARB) through the Clean Truck Check program, which combines vehicle reporting, an annual fee, and periodic emissions testing. Falling out of compliance can block your DMV registration and expose you to civil penalties of up to $10,000 per day.¹

Which Vehicles Are Covered

Clean Truck Check applies to almost all diesel and alternative-fuel heavy-duty vehicles with a gross vehicle weight rating (GVWR) over 14,000 pounds that operate on California public roads and highways.² That includes commercial trucks, buses, motorcoaches, government vehicles, and California-registered motorhomes. Every engine model year is covered, and vehicles running on natural gas, propane, or other alternative fuels are included alongside diesel.

Registration outside California does not exempt a vehicle. An out-of-state or foreign-registered truck that drives on California roads falls under the program from the moment it crosses the state line, and there is no low-use exemption for occasional entry.³

Three categories of vehicles are exempt:

Zero-emission vehicles (fully electric or hydrogen fuel-cell) with no tailpipe emissions.
Military tactical vehicles as defined under Title 13, CCR, Section 1905.
Emergency vehicles as defined under California Vehicle Code Section 165 or Health and Safety Code Section 1797.84.

Owners can also take a vehicle out of the program by placing it on Planned Non-Operation (PNO) status with the DMV and submitting the paperwork to CARB. A vehicle on PNO status cannot legally operate on California roads.³

Agricultural Vehicles Get a Lighter Schedule

Vehicles that qualify as agricultural test annually rather than semi-annually, so the definition matters. To qualify, a vehicle must be owned or operated by a farming business and used exclusively to transport agricultural products to their first point of processing.⁴

“First point of processing” means the location where harvested crops, livestock, or their products are first changed from their original state, such as packinghouses, cotton gins, slaughterhouses, and lumber mills. Distribution centers, retail locations, and any facility where the product has already been processed once do not count. A truck hauling oranges from an orchard to a packinghouse qualifies. The same truck hauling packed oranges from that packinghouse to a grocery warehouse does not.⁴

What Compliance Actually Requires

Three ongoing obligations keep a vehicle in good standing: report it, pay the annual fee, and pass emissions testing on schedule.

Reporting and the Annual Fee

Every covered vehicle must be reported in CARB’s online database, the Clean Truck Check Vehicle Inspection System (CTC-VIS), and the owner must pay an annual compliance fee. For 2026, that fee is $32.13 per vehicle, up from $31.18 in 2025.⁵ The fee must be paid before your compliance deadline to maintain active status. Vehicles can be reported with a temporary license plate if a permanent one hasn’t been issued yet.²

Testing Schedule and Test Types

Most covered vehicles must pass an emissions compliance test twice a year. California-registered motorhomes and qualifying agricultural vehicles test annually.² Each vehicle’s specific deadlines are set by its registration and reporting dates in CTC-VIS.

The test itself depends on engine model year. Diesel engines from 2013 and newer are OBD-equipped, and a CARB-credentialed tester scans the engine’s on-board diagnostics data using a CARB-certified device. The test can be performed anywhere; when a CARB-certified telematics device submits the data, a credentialed tester does not need to be physically present.⁶ Pre-2013 diesel engines get a smoke opacity test (the SAE J1667 snap-acceleration test used under the older Periodic Smoke Inspection Program), plus a visual and functional inspection of emissions control equipment.⁷

All heavy-duty diesel vehicles must also comply with CARB’s Truck and Bus Regulation, which required older engines to be retrofitted with a diesel particulate filter or replaced to meet the 2010 engine emissions standard. A vehicle that was never upgraded under that rule will fail Clean Truck Check testing regardless of how well the engine runs.⁸

If a vehicle fails, the owner must complete repairs and retest before the compliance deadline. An OBD test that returns “Not Ready” or “Invalid Test” is not a passing result. The vehicle needs to be driven further to complete its diagnostic readiness cycle, then retested.⁹ There is no automatic extension, so build in time for repairs before your deadline.

Buying or Selling a Covered Vehicle

Compliance follows the vehicle, not the owner, so a change in ownership does not reset the clock. A buyer inherits whatever compliance status the vehicle had at the time of transfer, but only if the vehicle met its compliance requirements within 90 days before the sale.³ If the seller let compliance lapse, the problem lands on the buyer.

For a brand-new vehicle, the purchaser must report it and pay the compliance fee within 30 days of purchase. The first emissions test is not due until the vehicle’s next scheduled testing date. Wait longer than 30 days to report, though, and the testing requirement kicks in immediately.³

Sellers must also include a specific written disclosure on the bill of sale notifying the buyer that the vehicle may be subject to CARB’s on-road or off-road diesel regulations and could face retrofit or replacement requirements. The seller must keep a record of the disclosure for three years, and the requirement applies even if the buyer plans to take the vehicle out of state.¹⁰

Out-of-State Operators

Out-of-state trucking companies are among the groups most likely to be surprised by these rules. CARB inspection teams test vehicles at border crossings, California Highway Patrol weigh stations, fleet facilities, and roadside locations.¹¹ A truck registered in Texas or Oregon carries the same testing and reporting obligations as a California-registered vehicle the moment it enters the state.

Owners cited for a Clean Truck Check violation during an inspection must pay the stated penalty and demonstrate correction within 45 calendar days, or 75 days for agricultural vehicles.¹¹ Correction can include documentation of a passing OBD or opacity test, repair invoices, parts receipts, or proof of reporting in CTC-VIS.

The Five-Day Pass

A non-compliant vehicle that needs to enter California briefly, for repairs or a one-time delivery, may qualify for a five-day pass through CTC-VIS. Each vehicle is eligible for one pass per calendar year, and the request must be submitted at least seven business days before entering the state.¹² The pass must be kept in the vehicle throughout the five-day window.

Two limits are worth knowing. The five-day pass does not make the vehicle compliant; its public lookup will still show non-compliant status, and it cannot be registered with the California DMV during the pass period. Vehicles with outstanding enforcement actions are not eligible at all.¹²

Freight Brokers Have Their Own Duties

Compliance reaches beyond vehicle owners. Freight brokers, meaning anyone who arranges transportation within California between carriers, shippers, and receivers, must verify that dispatched vehicles are Clean Truck Check compliant before booking them.¹³ These requirements are already in effect.

To verify, a broker must obtain one of two documents from the carrier: the vehicle’s individual compliance certificate from CTC-VIS, or an affirmation of fleetwide compliance issued within the past 12 months. Brokers must retain those records, along with the dispatching carrier’s business name, contact information, and address, for at least five years. CARB can request the records with as little as 72 hours’ notice.¹³ Brokers who dispatch non-compliant vehicles face their own enforcement exposure.

What Non-Compliance Costs

CARB uses several tools to find non-compliant vehicles before they reach a registration renewal. Roadside Emissions Monitoring Devices (REMDs) scan passing trucks for signs of excessive emissions, and Automated License Plate Readers cross-reference plates against CTC-VIS.² In-person inspections happen at weigh stations, border crossings, and fleet yards.

A vehicle flagged as a potential high emitter receives a Notice to Submit to Testing (NST). Once you receive an NST, you have 30 calendar days to submit a passing compliance test to CARB.⁷ The 30 days run from the date of the notice, not the date you open the mail.

Registration Holds

The DMV registration hold is one of CARB’s most effective enforcement tools. If your vehicle is not compliant with Clean Truck Check or the Truck and Bus Regulation, CARB can place a hold that prevents registration or renewal.¹⁴ You cannot complete registration until CARB verifies that the vehicle meets current requirements.¹⁵ A truck that cannot be registered is a truck that cannot legally work.

Civil Penalty Tiers

California Health and Safety Code Section 42402 establishes the civil penalty framework for air pollution violations, structured in tiers:

Up to $5,000 per day on a strict liability basis, applying to any violation of CARB rules, orders, or permits, with no requirement to prove intent or negligence.¹
Up to $10,000 per day, also strict liability, but the violator can raise an affirmative defense that the violation was not the result of intentional or negligent conduct.¹
Up to $15,000 per day when the violation causes actual injury to the health or safety of a considerable number of people.¹

Each day a violation continues counts as a separate violation, so exposure compounds quickly. Tampering with or removing emissions control equipment is a separate violation that carries additional penalties on top of any testing-related fines.

Reducing a Penalty

Owners who cooperate with CARB tend to fare better than those who ignore citations. Under CARB’s enforcement policy, penalties can be reduced based on several factors:¹⁶

Cooperating fully with an investigation and providing information promptly can reduce the penalty.
Inability to pay: CARB will review assets, revenue, and income, and may reduce penalties or set up a payment plan if the full amount would be an undue burden.
Voluntary disclosure: discovering and reporting a violation yourself within 21 days, then correcting it immediately, can reduce penalties by 25 to 75 percent.
Minor violations with no emissions impact that are quickly corrected can see reductions of 75 to 100 percent.
Supplemental environmental projects: CARB may allow you to offset up to 50 percent of a negotiated penalty by funding an approved environmental cleanup or air quality project.

The voluntary disclosure reduction is worth remembering. If you realize a vehicle in your fleet has been operating out of compliance, reporting it proactively and fixing it puts you in a stronger position than waiting for a roadside scan to find it.

Funding to Upgrade or Replace Vehicles

CARB’s earlier Truck Loan Assistance Program, which helped small-business fleet owners with 10 or fewer heavy-duty vehicles finance upgrades to engines meeting 2010 standards, closed to new enrollments on July 31, 2023.¹⁷

Current funding is aimed at the transition to zero-emission heavy-duty vehicles through the Zero-Emission Truck Loan Pilot Project and the Hybrid and Zero-Emission Truck and Bus Voucher Incentive Project (HVIP). HVIP provides vouchers that offset the purchase price of qualifying zero-emission trucks and buses, though voucher amounts are expected to decrease by about 5 percent per year as the market matures and vehicle costs decline.¹⁸ Fleet owners planning a long-term replacement strategy should check CARB’s incentive pages for current funding availability, since program details and eligible vehicle classes continue to change.

1
California Legislative Information. California Health and Safety Code HSC 42402
2
California Air Resources Board. Clean Truck Check – Overview Fact Sheet
3
California Air Resources Board. Clean Truck Check – FAQ
4
California Air Resources Board. Clean Truck Check – Agricultural Vehicles Requirements
5
California Air Resources Board. Clean Truck Check Compliance Fee Update Effective 1/1/2026
6
California Air Resources Board. Heavy-Duty Inspection and Maintenance Program (Clean Truck Check)
7
California Air Resources Board. Clean Truck Check Periodic Testing Requirements
8
California Air Resources Board. New California Requirements for On-Road and Off-Road Heavy-Duty Vehicles
9
California Air Resources Board. Clean Truck Check – Emissions Compliance Testing Requirements
10
California Air Resources Board. Disclosure FAQ – Regulation for In-Use Off-Road Diesel-Fueled Fleets
11
California Air Resources Board. Citations – TruckStop
12
California Air Resources Board. Five-Day Pass Request
13
California Air Resources Board. Clean Truck Check Requirements – Freight Contractor, Broker
14
California Air Resources Board. DMV Compliance Verification
15
California Air Resources Board. DMV Registration Notice with CARB Non-Compliant Vehicle Warning
16
California Air Resources Board. Enforcement Policy
17
CA.gov. Truck Loan Assistance Program
18
California Air Resources Board. Policy Workgroup for Fiscal Year 2025-26 Clean Truck and Bus Voucher Incentive Project (HVIP)