SYMPTOM GUIDE

Engine warning light on.

The amber engine warning light comes on briefly when you start the car and should then go out. If it stays on, the engine computer has stored a fault in the engine or the emissions system. If it flashes, it is usually a misfire that can damage the catalytic converter.

Can I keep driving?

Stop now
The light flashes with the engine running, comes on in red, or comes with smoke, loud noises, strange smells or high temperature.
Go to a garage soon
It stays on steady in amber and the car drives normally: you can finish your journey without flooring it or revving hard, and have it checked as soon as possible.
It can wait
It came on right after you checked the oil: make sure the dipstick is pushed fully home. If it is still on after a few trips, have it checked.

What it usually means

Misfire: On a petrol car, worn spark plugs or coils. It is what most often makes the light flash: unburnt fuel overheats the catalytic converter.
A sensor: The oxygen sensor, the mass airflow sensor or another engine sensor gives readings outside the normal range.
Emissions system: Catalytic converter, EGR valve, the diesel particulate filter or the AdBlue system.
Fuel injection: Injectors that fail or do not deliver the right amount of fuel.

What you can check yourself

Notice whether it is steady or flashing, and whether any other warning lights are on.
Notice whether the car drives differently: jerking, less power, noises, smoke or smells.
Read the fault codes with an OBD2 reader: the code tells you which system stored the fault.
Do not just clear the code: if the cause is still there the light comes back and the trail is lost.

What the garage confirms

Reading the codes and the sensors' live data to find the cause, not just the system.
Checking the spark plugs and coils, or the system the code points to.

If a fault warning light is on, find out what it is first: it can make the car fail the inspection.

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