A steady amber engine warning light means the car has found a fault and stored it. You can usually keep driving gently to a garage, and you should get it checked soon. A flashing light, or a red one, means stop: carry on and you can cause expensive damage.
The light does not say what is wrong. It says something is outside what the car expects. Here is how to read it, and what to do next.
What the colour and the behaviour tell you
- Steady amber: a fault has been recorded. Drive carefully, avoid hard acceleration and book a check soon.
- Flashing amber: usually a misfire, which can overheat and ruin the catalytic converter. Ease off, and stop somewhere safe if you can.
- Red: treat it as serious. Pull over safely, switch off and get help.
- Light plus loss of power, rough running, smoke or a smell: stop and get the car looked at.
Symbols differ between makes, so check your handbook for your car's version.
Common causes
- A loose or faulty fuel filler cap. Check it is tight first, as the light may clear after a few drives.
- A faulty oxygen sensor or other emissions sensor.
- Ignition problems such as a worn spark plug or a failing coil.
- A blocked or failing catalytic converter or DPF.
- Airflow or fuel system faults, from a dirty sensor to a leak.
Why it came on and then went off
The car re-tests itself, and if a fault does not happen again for a few drives the light may go out. The fault code stays stored though, and the cause is usually still there. It is worth having it read, because an intermittent fault tends to come back, and at a worse moment.
What a garage does about it
We connect diagnostic equipment, read the stored fault codes and then test the parts the code points to. The code is only a clue, so a good diagnosis checks the actual component before anything is replaced.
That matters because replacing parts by guesswork is how people end up paying for work they did not need. We explain what we find and what is needed, and we ask before we start. See our diagnostics service.
And your MOT
An engine management light on during the test is usually a fail. If your MOT is coming up, get the light looked at first. Our guide to why cars fail their MOT has more.
Quick answers
Can I drive with the engine light on?
If it is steady amber and the car drives normally, usually yes, gently and to a garage. If it flashes, or is red, stop.
Will the engine light fail an MOT?
It can. A lit engine management light is generally a reason to fail, so have it checked beforehand.
Can I just clear the light?
You can, but if the fault is still there the light comes back, and you have lost the record of what it was.
How long does a diagnostic check take?
Reading the codes is quick. Finding the cause can take longer, depending on the fault. We will tell you what we find.