What is Clean Truck Check?

Who must comply

Clean Truck Check applies to most diesel and alternative-fuel vehicles over 14,000 lbs GVWR operating on California roads, including vehicles registered out of state (source: CARB Clean Truck Check program page). Some vehicle categories are handled differently or excluded, so check your specific vehicle against CARB's program page.

Testing has been required since January 1, 2025

Passing periodic emissions compliance tests has been required since January 1, 2025 (source: CARB). How often you test, and by when, depends on your vehicle and reporting schedule — confirm yours with CARB.

OBD vs. smoke opacity testing

Vehicles with a compatible on-board diagnostics (OBD) system are tested by reading OBD data from the vehicle. Vehicles without usable OBD — typically older engines — are tested using a smoke opacity test that measures visible exhaust smoke under controlled conditions (source: CARB). Testers list which of the two they are equipped for; you can filter for either on this site.

What a credentialed tester is

A credentialed tester has completed CARB's training and exam and recertifies every two years (source: CARB). Only credentialed testers can submit compliance test results. Before you book, you can cross-check any business against CARB's public tester list.

How results are submitted

The tester submits the result electronically to CARB's Clean Truck Check system against your vehicle record, so you don't file it yourself (source: CARB). Keep your vehicle and account details accurate so the result lands on the right record.

Common questions

Who has to comply with Clean Truck Check?

The program covers most diesel and alternative-fuel vehicles over 14,000 lbs GVWR that operate on California roads, including out-of-state trucks. Check CARB's program page for the full applicability and exemption details.

When did testing become required?

Passing periodic emissions compliance tests has been required since January 1, 2025. Verify the current testing schedule that applies to your vehicle with CARB.

What's the difference between OBD and smoke opacity testing?

Vehicles with a compatible on-board diagnostics system are tested by pulling OBD data. Older vehicles without usable OBD are tested with a smoke opacity test that measures visible exhaust smoke.

What makes a tester credentialed?

A credentialed tester has completed CARB's training and exam and recertifies every two years. They submit results directly to CARB's system on your behalf.