The check engine light: what it means and what to do

The check engine light, also called the malfunction indicator lamp or MIL, is an amber engine-shaped symbol. It means the engine computer has found a fault that could raise the car's emissions. It does not say what the fault is. For that, the stored code must be read.

Steady light

A steady light means a fault has been confirmed, but it is not an emergency. If the car drives normally, you can keep driving carefully and have the code read in the next few days. Do not ignore it for long: a small fault such as a misfire can ruin an expensive catalytic converter.

Flashing light

A flashing light means a misfire severe enough to damage the catalytic converter is happening right now. Ease off the accelerator at once. If the flashing continues, stop when it is safe and have the car recovered. See engine misfire codes.

Red warnings are different

The check engine light is amber. A red oil can, a red temperature symbol or a red battery symbol means stop as soon as it is safe and switch the engine off. Those are not emission warnings. They warn of damage within minutes.

Simple checks you can do

1. Fuel cap. Tighten it until it clicks. A loose cap is one of the commonest reasons for the light. It can take a few days of driving for the light to go out.
2. Fluid levels. With the engine cold, check engine oil and coolant.
3. Recent work. If the light came on just after a service or repair, a plug or hose may have been left off. Tell the workshop.
4. How it drives. Note any shaking, loss of power, smoke, smell or noise, and when it happens. This helps the mechanic more than the code alone.

Getting the code read

Any workshop can read the code in a few minutes. You can also buy a small code reader that plugs into the diagnostic socket under the dashboard. See the OBD port and scan tools.

The light went out by itself

The computer keeps re-testing. If the fault does not come back over several trips, it switches the light off, but keeps the code in memory for a while. A fault that comes and goes is still worth mentioning at the next service.

Have a mechanic confirm. A fault code tells you which system reported a problem, not which part has failed. The same code can have several causes, and they differ between car models. Use this page to understand the code, then have a qualified mechanic test the car before any part is replaced.