Engine Management Light (EML): What It Means

If your engine management light (EML) has come on, you might be wondering whether you can keep driving, what’s causing it, and if it means your car will fail its MOT.

This article will take a look at what the engine management light means. In particular the common causes and what you should do next if that light comes on. 

What is the engine management light?

The EML - sometimes called the check engine light or engine warning light - is a dashboard symbol that looks like the outline of an engine.

It’s controlled by your car’s engine control unit (ECU), which uses sensors to monitor performance and emissions. If a fault is detected, the ECU switches the light on.

What does each type of engine management light mean?

Is it safe to drive with the engine management light on?

• Solid amber: Usually safe to continue driving carefully but get your car checked sooner rather than later.
• Flashing amber: Best to stop as soon as possible. Continuing to drive can cause expensive damage.
• Red: Do not drive. Stop immediately in a safe place and call for assistance.

What causes the engine management light to come on?

• Oxygen sensor fault: Monitors fuel/air mix. If faulty, it can affect emissions and fuel economy.
• Catalytic converter issues: A damaged or clogged converter can trigger the EML and lead to poor performance.
• Diesel particulate filter (DPF) blockage: Common in modern diesels. If blocked, it can cause the EML to illuminate.
• Mass airflow sensor fault: Measures air entering the engine. Faults can upset the fuel-air mix.
• Ignition system problems: Faulty spark plugs or coils can trigger the EML, often with rough running or misfires.
• Loose fuel cap: Surprisingly common - vapour leaks can cause the ECU to switch on the warning light.
• Blocked fuel pump: Can reduce fuel flow, causing loss of power and warning light activation.
• Clutch/gearbox issues: Sensor faults or slipping clutches can activate the EML.
• General sensor failures: Modern cars rely on many sensors. A faulty reading can trigger the light.

Estimated repair costs

• Spark plugs: £50–£150
• Mass airflow sensor: £200–£400
• Catalytic converter: £600+
• DPF replacement: £1,000+

Does an engine management light mean MOT failure?

Yes - if the engine management light stays on, it’s classed as a major fault and will result in an MOT failure.

Exceptions:

• Petrol cars registered before 1 July 2003
• Diesels registered before 1 July 2008

How to reset the engine management light

• Switch the car off, wait a few minutes, and restart - sometimes clears temporary faults.
• Check obvious causes (loose fuel cap, dipstick not secured).
• If the fault persists, an OBD-II scanner can read and clear codes, but the light will return unless the issue is fixed.
• Best practice: have a mechanic diagnose and repair the problem.

Paying attention to your engine management light helps prevent costly repairs and ensures your car remains safe and roadworthy.