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

8 comments on “Expert advice: what an engine warning light means and what to do

  1. Jacob Miller 31/05/2018 6:25 AM

    Very useful post. Many times the check engine light pops on and it comes without warning. If you see the check engine light on or blinking, either way, you should have the vehicle checked by a Qualified Service Technician as soon as possible. Thanks for the tips.

  2. Julie Wern 16/01/2019 12:19 PM

    Really nice article. Check engine light is nothing but an early warning system which indicates that certain components of the engine are not working in a way they should have which needs to be fixed immediately to prevent any major problems. The vehicle should be diagnosed by a well-trained technician. However, some people often ignore the appearance of such sign which could have a disastrous impact on the performance of the vehicle.

  3. Jenny Parker 05/03/2019 10:53 AM

    Malfunction of certain components of the engine like oxygen sensor, catalytic converter or spark plug leads to the appearance of the check engine light. Such abnormality may not have immediate consequences but could have a disastrous impact on the performance of the vehicle if ignored. So, it is really essential to spot and fix mechanical issues in time to keep the vehicle in working order. Skipping such kinds of maintenance could bring the vehicle to a halt in the middle of nowhere. Regular maintenance is the key to keep the vehicle in working order. However, some people don’t pay proper attention to the vehicle which could be very dangerous.

    • Steve HURFORD 09/04/2019 7:30 PM

      My radiator/water level light has been on for 5 years. I’ve been told repeatedly by mechanics that is just the sensor light that is faulty. Seem to recall seeing any warning lights on, the car will be failed on the MOT. Anyone know if this is correct????

      • Swisher 10/04/2019 3:30 PM

        Some warning lights are an immediate fail (engine management, oil) but others are seen as minor faults rather than major faults, and are just advisories. Either way you should get it fixed ASAP because you need to know when it happens for real!

  4. Chris Pritchard 08/04/2019 9:02 PM

    If you have an older car and experience engine warning lights frequently, it may be worth investing in an OBD2 reader and Haines manual of computer code faults. A decent one can be around £60, and will give you instant fault analysis. The garage mechanics equipment is far more costly and gives much better information, but the cheaper ones give good results.

  5. Mavis Evans 10/04/2019 5:38 AM

    I had this light come on and all the mechanic did was just undo the battery lead for a few minutes and reconnect. Bingo! All was ok. Only had to reset the clock..

  6. dave 11/04/2019 5:55 PM

    These new fangled cars are a blooming nuisance give us back the old ford pops with just an oil warning light and a petrol tank gauge “ah well one can dream can”t one”.

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