Fleet Emissions Uncertainty: What California's Delays Mean for Truck Buyers

Fleet owners and commercial vehicle buyers need to understand California's CARB regulations to avoid costly penalties and downtime. The California Air Resources Board's emissions rules affect all heavy-duty trucks operating in the state—and knowing which ones are in force (and which are paused) helps you make smarter, lower-risk purchases.

This guide breaks down what’s still required, what’s on hold, and how to buy trucks that stay compliant amid changing rules.

What’s Still Required Under CARB Rules

California’s CARB regulations set the bar for trucks allowed to operate in the state. These requirements have been in effect since December 2008 to reduce air pollution from commercial vehicles.

While some new rules are delayed, the three main regulations are still active and enforced.

1. Engine Year Rule

The Truck and Bus Regulation requires all diesel trucks over 14,000 pounds Gross Vehicle Weight Rating (GVWR) to have a 2010 or newer engine.

• Low-use exemption: Under 1,000 miles per year in California.
• Penalty: Non-compliant trucks can’t renew DMV registration or legally operate.

2. Clean Truck Check Testing

Clean Truck Check is California's emissions testing program for heavy-duty vehicles.

• What to do: Trucks over 14,000 pounds GVWR must use a CARB-certified tester for semi-annual testing.
• How it’s enforced: Roadside sensors monitor emissions and flag high-polluting vehicles for immediate checks.

3. Out-of-State Trucks Must Comply

All trucks operating in California must comply with CARB rules, even if registered elsewhere. The compliance deadline for your vehicle depends on where it is registered.

• California-registered vehicles: Tied to your annual DMV registration renewal date
• Out-of-state vehicles: Based on the last digit of your Vehicle Identification Number (VIN)

Recent Changes in CA Emissions Rulemaking

CARB has temporarily paused enforcement of some new rules until they receive federal approval from the EPA. These delays don’t affect existing engine or testing requirements, but they do influence which new trucks are available to buy right now.

Advanced Clean Fleets (ACF)

Advanced Clean Fleets (ACF) transitions fleets to zero-emission vehicles. However, CARB paused ACF enforcement for reporting and registration until the EPA grants a Section 209(b) waiver.

What it means: Fleets can delay zero-emission reporting for now, but the requirement will resume once federal approval lands.

Heavy-Duty Omnibus

This sets stricter standards for nitrogen oxide (NOx) and particulate matter emissions from new diesel engines. Other regulations primarily affect manufacturers, but they influence which new trucks are available for purchase.

• Advanced Clean Trucks (ACT): Requires manufacturers to sell increasing percentages of zero-emission trucks
• Heavy-Duty Omnibus: Sets stricter emissions standards for new diesel engines

For industry context on how manufacturers are adapting to changing emissions requirements, see OEM articles on Comvoy.

How CARB Enforces Compliance

CARB’s enforcement uses inspections, notices, and fines to keep fleets in check. Here’s who’s responsible:

• Motor Carriers: Ensure all fleet vehicles are compliant, registered with CARB, and have passed required tests
• Drivers: Provide compliance documentation during roadside inspections
• California Shippers and Receivers: Verify that hired carriers meet CARB requirements

If you get a “Notice to Submit to Testing,” you have 30 days to provide passing results from a certified tester. Ignoring it can mean steep fines and blocked registrations.

What to Buy Now With Less Regulatory Risk

The smartest fleet strategy right now is simple: buy trucks that already meet 2010 or newer standards. This ensures immediate compliance while keeping options open for future zero-emission transitions. You should also consider the Section 179 truck regulations before making a decision.

Pro Tip

Use smart search filters to identify compliant vehicles quickly. Comvoy's vocation-specific search filters help you find trucks with 2010 or newer engines that match your job requirements, whether you need it for delivery or you’re looking for the best snow plow trucks.

For more information, read our guide on Navigating Your Options: Key Tips For Choosing The Right Commercial Vehicle. 

Keep Your Fleet Moving With Transparent Listings

Staying compliant starts with sourcing the right vehicles, and Comvoy provides transparent listings with comprehensive vehicle specifications to help you find work-ready trucks and vans that meet California's standards. 

Explore electric commercial vehicles for your fleet to future-proof your operations or implement fuel-efficient fleet strategies for current needs. Our platform connects you with compliant options. You can also check the key considerations for fleet electrification.

FAQ

What engine model years are legal for diesel trucks over 14,000 lbs GVWR in California?

Diesel trucks and buses with GVWR over 14,000 pounds must have 2010 or newer model year engines. Vehicles operating less than 1,000 miles annually in California may qualify for a low-use exemption.

No. All trucks must be CARB-compliant to operate in California, regardless of their home state, to avoid registration denial and citations.

No, all heavy-duty trucks operating in California must meet CARB requirements regardless of registration state. Non-compliant vehicles face registration denial and citations.

How often do trucks need Clean Truck Check emissions testing?

Most heavy-duty vehicles are required to undergo emissions compliance testing twice a year. Vehicles with 2013 or newer engines will eventually require testing four times a year. You should consider this when you’re considering the best time to buy a truck.

Is the Advanced Clean Fleets rule being enforced right now?

CARB issued an enforcement discretion notice pausing ACF reporting and registration requirements while awaiting EPA waiver approval. Check CARB's website for the current enforcement status.

What penalties apply for missing emissions tests or failing inspections?

Penalties include fines and potential DMV registration blocks until compliance issues are resolved. Violations can also result in Notice to Submit to Testing requirements.

Sources:

1. California Air Resources Board. Truck and Bus Regulation. https://ww2.arb.ca.gov/our-work/programs/truck-and-bus-regulation
2. California Air Resources Board. Clean Truck Check Emissions Compliance Testing Requirements. https://ww2.arb.ca.gov/clean-truck-check-emissions-compliance-testing-requirements
3. California Air Resources Board. Advanced Clean Trucks Credit Summary Through 2024 Model Year. https://ww2.arb.ca.gov/advanced-clean-trucks-credit-summary-through-2024-model-year
4. U.S. Government Publishing Office. Section 209(b) Waiver. https://www.govinfo.gov/content/pkg/FR-2025-01-06/pdf/2024-31125.pdf

California Air Resources Board. Clean Truck Check FAQ. https://ww2.arb.ca.gov/resources/fact-sheets/clean-truck-check-faq-0