In California, a lit check engine light fails the smog check. The light means the computer has stored a fault. Fix the cause, confirm the light stays off and then test.
Key takeaways
- Lit light means automatic failure.
- Diagnose first.
- Let monitors reset after repair.
Why the light fails the test
The smog check reads the onboard computer. If the computer says there is an emissions-related fault, the car fails by definition.
What triggers it
Misfires, oxygen sensors, a loose gas cap, a failing converter or a sensor wiring fault all set the light. Our diagnostics page explains how we find the cause.
After the repair
Once the fault is fixed, the light turns off after the computer confirms the problem is gone. Monitors then need to complete.
Do not shortcut it
Clearing the light does not fix it, and monitors reset to not ready.
One-stop approach
We diagnose, repair and test in the same building.
What a technician looks at after the code
A code names the system. The technician then checks live sensor data, inspects hoses and wiring and runs tests on the suspect component. For a misfire code, that means checking plugs, coils and injectors. For an evap code, it means smoke testing. For a catalyst code, it means checking oxygen sensor response and exhaust leaks. Each step either confirms or rules out a cause, which is why diagnosis beats guessing.
Getting the light off for good
After the repair, the light goes off once the computer confirms the fault is gone, which can take several drives. Then the readiness monitors need to complete. We check that the light is off and the monitors are ready before recommending a retest. Rushing back too early is the most common reason for a second not-ready result.
Need help in south Bakersfield?
Questions about check engine light? Read our Check Engine Light page, call (661) 599-9098 or request a time. Peña's Auto Electric, Smog & Repair, 303 Taft Hwy, Suite B, Bakersfield, CA 93307. Mon to Fri 9:30 AM to 5:30 PM, Sat 8 AM to 1 PM.
Frequently asked questions
Will it pass with the light on?
No.
Can I clear the light and test?
The monitors would not be ready.
What if the light is flashing?
Stop driving at speed and have it checked.
How soon after repair can I test?
When monitors are ready.
Related reading
Sources
- California Bureau of Automotive Repair, Smog Check program and consumer information