Engine Warning Light On: What It Means and What to Do

The engine warning light, also called the engine management or check engine light, means the car's computer has detected a fault in the engine or emissions system. A steady light usually means get it checked soon. A flashing light usually means a serious misfire, so reduce speed and have it looked at straight away.

What does the engine warning light look like?

On most cars it is an amber outline of an engine. Some cars show the words "check engine" instead. It is part of the on-board diagnostics system, which monitors the engine and emissions sensors and stores a fault code when something is outside its normal range.

What usually causes it?

• a faulty sensor, such as an oxygen (lambda) sensor or airflow sensor;

• ignition problems, such as worn spark plugs or a failing coil pack on a petrol car;

• a blocked diesel particulate filter on a diesel;

• a problem with the exhaust gas recirculation (EGR) valve;

• a loose or faulty fuel filler cap on some cars;

• a catalytic converter fault.

The light alone does not tell you which of these it is. A diagnostic check reads the stored fault code, which points to where the problem is.

Is it safe to keep driving?

• Steady light, car driving normally: you can usually drive carefully to have it checked, but do not leave it for weeks.

• Flashing light: this often means a misfire, which can overheat and damage the catalytic converter. Reduce speed and get it checked as soon as possible.

• Light plus loss of power, smoke, strange noises or a red warning light: stop when it is safe and get help.

Some cars go into a reduced-power "limp mode" to protect the engine. If that happens, avoid motorways and get the car checked.

Will the engine warning light cause an MOT failure?

It can. An engine management light showing a fault can lead to an MOT failure, so it is worth getting it sorted before the test. Our MOT checklist covers what else to check.

Can I just clear the code myself?

You can buy code readers, and clearing a code will turn the light off for a while. But if the fault is still there, the light will come back, and clearing codes just before an MOT does not hide a fault for long because the system needs to complete its own checks first. It is better to find and fix the cause.

Common questions

Why did the light go off on its own?

Some faults are intermittent, so the light can come and go. The fault code is usually still stored and worth reading.

Does a lit engine light affect fuel economy?

It can. Faulty sensors or misfires can make the engine run less efficiently, so you may use more fuel.

What other warning lights should I know about?

Our guide to dashboard warning lights explains the most common ones and what to do.

Engine warning light on in Barnsley?

anycolourcar.com has a service centre in Barnsley, South Yorkshire, where we can read fault codes and find the cause. Our labour rate is £80 per hour plus VAT. Find out more on our servicing and repairs page or call 01226 574321.

Updated October 2026.