Engine management light on? What to do

The engine management light, usually an orange or amber engine-shaped symbol on the dashboard, is one of the warning lights drivers worry about most. It doesn’t always mean something serious, but it does mean the car has found a fault, and it shouldn’t be ignored.

What the light is telling you

Modern engines are run by a computer that watches dozens of sensors. When it spots a reading that’s out of range, it stores a fault code and switches on the engine management light, often called the EML or check engine light.

The code tells a mechanic where to start looking, not necessarily which part has failed. A code pointing at a sensor, for example, can be caused by the sensor itself, its wiring, or a fault elsewhere that the sensor has picked up. That’s why a proper diagnosis is worth more than just reading the code.

Steady or flashing?

A steady light means a fault has been detected. If the car is driving normally, it’s usually fine to carry on carefully and get it checked soon. If it has lost power, is running roughly or feels different, keep journeys to a minimum until it’s been looked at.

A flashing light is more urgent. On most cars it means the engine is misfiring badly enough to damage the catalytic converter, which is expensive to replace. Ease off, avoid hard acceleration, and get it checked as soon as you can.

Warning lights vary between makes, so check your handbook for what yours means. And if a red warning light comes on, such as oil pressure or engine temperature, stop as soon as it’s safe and switch off.

Common causes

There are hundreds of possible fault codes, but these are among the usual suspects:

• Faulty sensors, such as oxygen (lambda), airflow or temperature sensors
• Misfires from worn spark plugs, ignition coils or injectors
• Exhaust gas recirculation (EGR) valve faults
• A blocked diesel particulate filter (DPF), especially on diesels that mostly do short trips
• Catalytic converter problems
• Wiring or connector faults
• On some cars, a fuel cap that isn’t closed properly

Will it fail the MOT?

Yes. An engine management light that’s showing a fault is a major defect, so the car will fail. The same goes if the light doesn’t work at all: it should come on when you turn the ignition on, then go out. This applies to petrol cars first used from 1 July 2003 and diesels first used from 1 July 2008, hybrids included.

So if the light is on, get it looked at before your MOT rather than at it.

Getting it diagnosed

We charge £60 + VAT for an engine management light diagnostic. If you’d just like us to take a quick look at the problem first, that’s £15 + VAT.

If a repair is needed, we’ll price it for you. We carry out diagnostics and repairs on all makes and models of cars and light commercial vehicles.

Before you bring it in

A few details help us find the fault faster:

• When the light first came on, and whether it’s steady, flashing or comes and goes
• Anything else you’ve noticed, such as loss of power, rough running, smoke or a change in fuel economy
• Whether it came on after refuelling, a long run or a cold start
• Any recent work on the car

Useful links

• Diagnostics
• Car repairs
• MOTs
• MOT inspection manual: noise, emissions and leaks (GOV.UK)
• Check if a vehicle has been recalled (GOV.UK)