The Clean Truck Check program, starting in early 2025, will enforce new rules for vehicle emissions testing. These rules focus on On-Board Diagnostic (OBD) system readiness and Permanent Diagnostic Trouble Codes (PDTC). The goal is to reduce emissions and improve air quality by making sure vehicles are properly checked and repaired.  

In simple terms, readiness means that a vehicle’s internal tests, across different OBD systems, are complete. PDTCs are trouble codes that show unresolved issues in the vehicle. Unlike other codes, PDTCs can’t be cleared without actually fixing the problem. Clearing codes before the test will now cause the vehicle to fail.  

During a 2023 pilot phase, vehicles failed only if the “Check Engine” light was on, but some vehicles with unresolved problems or incomplete OBD tests still passed. About 20% of drivers were clearing codes just before testing, which will no longer work under the new rules starting in 2024. Vehicles with incomplete tests or unresolved issues will now fail.   

Key points to know: 

• OBD readiness checks whether a vehicle’s system tests are complete. If a vehicle has recently cleared codes, these tests may not be finished, causing the vehicle to fail.

• PDTCs are trouble codes that stay on until the issue is fully repaired and confirmed through drive time.

• Clearing codes just before testing will result in test failure since the vehicle’s systems need time to run their test.

To pass the Clean Truck Check OBD test:

Address any “Check Engine” light issues promptly, test early to allow for re-testing if necessary, and avoid clearing codes to ensure your vehicle completes its diagnostic tests, as incomplete tests can fail.

For more information, visit: https://ww2.arb.ca.gov/obd-readiness-criteria.