Does an Engine Management Light (EML) Fail an MOT?

In short, yes. If your EML is on during your MOT test, it will be classed as a major fault and an MOT failure. 

So, it’s crucial to get your car checked over before your MOT test, even if you only have a minor engine issue.

If your car has a dangerous fault (which it may do if your EML is red) and you are found to be knowingly driving a vehicle in a dangerous condition, you could be subject to a £2,500 fine.

An engine management light, or EML, is one of a few dashboard lights that illuminate and/or flash when your car’s sensors detect a potential engine, exhaust, or emissions system issue. It’s sometimes referred to as a “check engine light”.

If your car’s sensors detect an issue — or, if you have a broken sensor — they’ll tell the engine control unit (ECU), which will trigger the EML to switch on.

Unlike your other dashboard warning lights, an illuminated engine management light won’t tell you exactly what the issue is. So, it’s important to take your car to a professional mechanic for a thorough diagnosis. 

If your EML turns on when you start your car but turns back off after a few seconds, this is normal, and you won't fail your MOT test. But, if your EML stays on or illuminates while you’re driving, this points to potential issues.

There are three types of engine warning lights to watch out for: amber lights, flashing amber lights, and red lights.

Amber light

A steady amber or orange light usually indicates a minor vehicle issue. 

While you can safely continue your journey if your amber light is switched on, try to get your car to a garage as soon as you can to prevent further damage. 

Flashing light

A flashing amber light points to a more serious issue that’s affecting your car’s performance, such as an engine misfire. It’s often accompanied by a difference in the way your car handles or drives, for example, if your car starts juddering or making unusual sounds. 

A flashing amber light should be treated as a matter of urgency. Take your car immediately to a professional mechanic to be checked over if it’s capable of handling the distance. Alternatively, drive home and call a mobile mechanic.

Red light

Some cars will only show amber or flashing amber for EML faults. However, depending on the make or model you may also see a red light. A red engine management light indicates a critical engine or emissions system issue that requires immediate attention. 

If your EML illuminates red, your car isn’t safe to drive. Pull over in a safe place immediately, turn off your engine, and call your breakdown provider.

Bear in mind that even with fully comprehensive car insurance, you might not have breakdown cover. So, compare car insurance policies to find a provider that offers breakdown cover as an add-on for peace of mind. 

There are lots of reasons why your EML might turn on, ranging from simple fixes to complex issues. Here are some common causes:

Catalytic converter issues 

The catalytic converter filters out harmful car emissions, transforming carbon monoxide and other toxic gases into less harmful substances. It’s susceptible to leaks, clogs, physical damage, and various issues that can damage or break the device and trigger your EML.

Malfunctioning oxygen sensor

Oxygen sensors monitor the unburnt oxygen travelling through the car exhaust. If your engine is burning too much or too little fuel, the oxygen sensors will tell your ECU, switching on your engine management light.

Mass airflow sensor failure

The mass airflow sensor measures and monitors the air entering your engine. A faulty airflow sensor or a missing, damaged, or clogged airflow filter will create an unbalanced air/fuel mixture. Left unchecked, this can cause issues like engine stalling, engine hesitation, and severe engine damage.

Ignition system fault

Faulty spark plugs, malfunctioning ignition coils, and crank position sensor failures are common ignition system faults that can trigger your car's engine management light to turn on. You might have difficulties starting your vehicle or experience engine misfires, stalling, loss of power, and breakdowns. 

Blocked diesel particulate filter

Diesel vehicles may have a diesel particulate filter (DPF). The DPF blocks and filters out soot from your exhaust to reduce harmful emissions. If it gets blocked or there’s a fault with the differential pressure sensor, you might get an EML warning.

The cost of repairing an illuminated engine warning light depends on the underlying issue that caused it to switch on, along with your car’s make and model. 

A simple issue like replacing your ignition coils may cost between £70-£220. Complex issues like a catalytic converter replacement can cost you anywhere from £150 to £900. 

It might sound steep. But if you know what happens if you fail your MOT test, you’ll know that it’s cheaper to fix your car beforehand. Plus, you’ll avoid any potential fines.

Does comprehensive car insurance cover EML repairs? 

Many issues that cause the EML to turn on are caused by poor maintenance, which isn’t covered by comprehensive car insurance. However, if the fault was the direct result of an accident or fire, you should be able to get the cost covered.