What does the check engine light mean?
What It Means
The check engine light (CEL) is part of your car's onboard diagnostics (OBD-II) system. When the computer detects an issue, it stores a trouble code and turns on the light. The light can be steady or flashing; a flashing light usually indicates a severe misfire that can damage the catalytic converter, so you should stop driving as soon as it's safe.
Common causes include a loose or faulty gas cap, oxygen sensor failure, catalytic converter issues, mass airflow sensor problems, spark plug or ignition coil faults, and vacuum leaks. The exact cause can only be determined by reading the trouble codes with an OBD-II scanner.
- Loose or damaged gas cap
- Faulty oxygen sensor
- Catalytic converter failure
- Misfiring spark plugs or ignition coils
- Mass airflow sensor issues
- Vacuum leaks
What to Do
If the light is steady, you can usually continue driving, but you should have the codes read soon to diagnose the issue. Many auto parts stores will read codes for free. If the light is flashing, reduce power and stop driving as soon as possible to prevent damage.
Once you have the codes, you can research the specific code or take the car to a mechanic. Ignoring a check engine light can lead to failed emissions tests, reduced fuel economy, and more expensive repairs down the road.
- Check if the gas cap is tight
- If steady, drive cautiously and get codes read
- If flashing, stop driving and seek service immediately
- Do not disconnect the battery to clear the light; it will come back if the issue persists
Common mistakes
- Thinking a steady check engine light always means a minor issue; it can indicate serious problems.
- Clearing the code by disconnecting the battery without fixing the problem; the light will return.
- Ignoring a flashing check engine light, which can cause costly catalytic converter damage.
