Expert advice: what an engine warning light means and what to do

Engine warning light

This March we saw a significant increase in the number of customers ringing us with their engine warning light on. These faults were up by more than a third (39.3 per cent) compared with February.

Warning lights can be worrying and frustrating in equal measure. They’re a worry because they indicate trouble. And when things go wrong with cars, it usually costs money. They’re frustrating because while the lights reveal a fault, they don’t tell you exactly what the problem is. Here’s what you need to know.

What does an engine warning light signify?

The trouble with the engine warning light is that it can come on because of a plethora of problems. It might be a serious fault, or it might be something really innocuous. The annoying thing is that for we drivers, the outcome is the same orange light. And the fact that it’s a diagram of a little engine glowing an ominous orange doesn’t help!

Why does the warning light come on?

Modern cars are packed with sensors. These relay information back to the car’s computer. If this detects something abnormal, one of many dashboard warning lights illuminates. If it’s an engine warning light, it might come on simply because of a faulty sensor. It may be a sensor measuring coolant temperature, air temperature or pressure in the engine’s inlet manifold. It might be measuring the oxygen before and after exhaust gases have been through the catalytic converter. Or it might be the sensor measuring the airflow to the engine.

What happens if a warning light comes on?

While orange lights are alerts rather than red ‘stop driving now!’ signals, you still need to get to the bottom of why the engine light has come on. The trouble is, the warning light might be the only symptom of a fault.

But while your vehicle could still be driving normally there’s no guarantee that’s going to last. Contact a garage, explain the problem and make an appointment. As garages can find out what’s wrong very quickly, there’s no reason why they shouldn’t see you at short notice.

How can problems show themselves?

Engine warning light

Ignore an engine warning light and this could be the result (Picture iStock/south_agency)

Your orange warning light might be accompanied by your car misfiring. This is when one or more cylinders doesn’t fire in time and it makes the engine sound rough. There might be smoke coming out of the exhaust and your engine may lose power. If this happens pull over as soon as it’s safe to do so. Your engine really is telling you something’s wrong and continuing to drive could damage it. Then call your breakdown service. Read our expert advice on dealing with a breakdown.

What a technician will do

The brilliant thing about the engine warning light is that it will have been initiated by the car’s computer. That means the car will have a record of why it’s turned the light on. In turn that will enable a technician to diagnose the fault.

They will do this by plugging a computer into the car’s OBD or On-Board Diagnostics port. This will find the fault code that the car’s computer has logged and the technician will be able to tell what the problem might be and hopefully fix it. At this point, all we as drivers can do is hope and pray that it isn’t serious!

Scott Wilson is vehicle and customer data insight manager for Green Flag

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