CARB Compliance & Clean Truck Check Testing in California's Central Valley

California's air quality regulations are among the most comprehensive in the United States, and the California Air Resources Board (CARB) plays a central role in enforcing emissions standards for commercial vehicles. For fleet owners, trucking companies, and heavy-duty vehicle operators throughout the Central Valley, understanding applicable CARB requirements — and staying current on testing — is a critical part of operating legally in the state.


ST Pros helps eligible commercial fleets, semi-trucks, and RVs throughout California's Central Valley meet applicable CARB Clean Truck Check emissions testing requirements through our convenient mobile testing service. We come directly to your location, so you're not dealing with the hassle of scheduling facility visits or pulling trucks out of service to get to a test station.

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What Is the CARB Clean Truck Check Program?

The California Air Resources Board's Clean Truck Check program — also known as the Heavy-Duty Inspection and Maintenance (HD I/M) Program — requires many heavy-duty commercial vehicles operating in California to undergo regular emissions compliance testing. The program is designed to identify and address excessive emissions from trucks and other heavy-duty vehicles that contribute to air quality issues throughout the state.


A Clean Air Check vehicle is a commercial, private, or government-owned truck or heavy-duty vehicle that is subject to emissions compliance testing under this program. Clean Air Check testing measures a vehicle's actual on-road emissions performance and helps ensure that trucks operating in California meet applicable emissions standards.

Who Needs CARB Clean Truck Check Testing?

Many heavy-duty vehicles operating in California are subject to Clean Truck Check requirements. This generally includes commercial trucks, fleet vehicles, semi-trucks, and certain other heavy-duty vehicles. Testing requirements can vary based on the vehicle type, model year, fuel type, and equipment. If you operate commercial vehicles in California's Central Valley and are unsure whether your vehicles are subject to testing, contact ST Pros — we can help you understand the applicable requirements for your fleet.

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How Often Is Testing Required?

Most vehicles currently subject to California's Clean Truck Check program require emissions compliance testing twice per year. Beginning October 1, 2027, OBD-equipped vehicles will be required to complete testing four times per year. Testing requirements can vary based on vehicle type and equipment. ST Pros provides mobile Clean Air Check testing to help eligible fleet owners and vehicle operators stay ahead of their applicable testing schedule.

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What Happens If a Vehicle Fails Testing?

If a vehicle fails its Clean Air Check, the owner will typically need to have the vehicle repaired to bring emissions into compliance and then return for a follow-up test. Maintaining a current testing schedule and addressing emissions issues promptly is important for keeping commercial vehicles legally operating in California. ST Pros can provide testing documentation to assist you with your compliance records.

How ST Pros Helps With CARB Compliance

ST Pros provides mobile Clean Air Check testing for eligible commercial fleets, heavy-duty vehicles, semi-trucks, and RVs throughout California's Central Valley. Our mobile testing service is designed to make the required testing process as efficient as possible for fleet operations:

We come directly to your fleet location — no facility visits required

Multiple vehicles can be tested in a single scheduled visit

Results submitted to the state system within 24 hours

Fleet pricing available for multi-vehicle testing visits

20+ years of commercial vehicle testing experience in the Central Valley

Licensed and insured mobile testing professionals

ST Pros provides mobile testing assistance for applicable CARB Clean Truck Check requirements. For complete and authoritative information about the Clean Truck Check program, vehicle-specific testing requirements, and compliance obligations, we recommend consulting the California Air Resources Board directly at arb.ca.gov.

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CARB Compliance FAQs

  • How does ST Pros help with CARB compliance?

    ST Pros provides mobile Clean Air Check testing for eligible commercial fleets, heavy-duty vehicles, semi-trucks, and RVs throughout California's Central Valley. We come directly to your location, making it easier to complete required emissions testing while helping minimize downtime for your drivers and fleet. Our mobile testing service is designed to help vehicle owners and fleet managers stay on top of applicable CARB Clean Truck Check testing requirements.

  • How frequently is CARB testing required?

    Most vehicles subject to California's Clean Truck Check program currently require emissions compliance testing twice per year. Beginning October 1, 2027, OBD-equipped vehicles will be required to complete testing four times per year. Testing requirements can vary based on vehicle type and equipment. Contact ST Pros at 559-824-4291 for more information about your specific vehicles.

  • What happens after a Clean Air Check is completed?

    Once your Clean Air Check is completed, the test results are submitted to the state and the applicable records are updated in the system. This helps keep your vehicle's Clean Truck Check compliance information current and allows you to stay on top of applicable CARB requirements.

  • Are semi-trucks subject to CARB Clean Truck Check requirements?

    Many semi-trucks and heavy-duty commercial vehicles operating in California are subject to Clean Truck Check requirements. Requirements can vary based on the specific vehicle type, model year, fuel type, and equipment. ST Pros provides mobile Clean Air Check testing for eligible semi-trucks and can help you understand the applicable requirements for your vehicles.

Questions About CARB Compliance? Call or Text ST Pros at 559-824-4291 — We're Here to Help.