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Does an Engine Management Light (EML) fail an MOT

December 12, 2023

Has your car’s Engine Management Light (EML) turned on and left you wondering whether your car will pass the MOT test? This is a common concern among drivers as the EML is an important indicator of potential issues with your vehicle's engine, and it could lead to an MOT failure if not addressed properly.

Here's what you need to know about the Engine Management Light and what you can do if the EML has turned on.

What is an Engine Management Light (EML)?

The EML, also known as the check engine light, is a dashboard warning light that illuminates when your vehicle’s sensors detect a potential issue with the engine or emissions system.

If your vehicle has a flashing or continuous Engine Management Light, it’s best to seek professional help.

Car dashboard showing the engine management light on

5 most common reasons that can cause the Engine Management Light to turn on

Although there are a wide range of reasons that can cause the Engine Management Light to turn on, these are the most common:

1. Performance issues

  • Oxygen sensor malfunction: the oxygen sensors monitor the levels of unburned oxygen in the exhaust and helps to adjust the air-fuel mixture for optimal efficiency
  • Mass airflow sensor failure: the mass airflow sensor measures the amount of air entering the engine
  • Spark plug or ignition coil problems: faulty spark plugs or ignition coils can cause misfires, poor performance, and increased emissions
  • Vacuum leaks: vacuum leaks can disrupt the proper functioning of the engine's air-fuel mixture
  • Faulty fuel injectors: damaged or clogged fuel injectors can lead to poor engine performance
  • Malfunctioning throttle position sensor: this sensor monitors the position of the throttle and helps the vehicle control the air-fuel mixture

2. Emission control issues

  • Catalytic converter issues: the catalytic converter reduces harmful emissions from the exhaust
  • Exhaust gas recirculation (EGR) valve malfunction: the EGR valve recirculates a portion of the exhaust gas back into the engine to reduce nitrogen oxide emissions

3. Fuel efficiency issues

  • Loose or damaged fuel cap: a loose or damaged fuel cap can cause fuel vapours to leak which can trigger the EML to turn on

4. Overheating issues

  • Engine coolant temperature sensor failure: this sensor monitors the engine's temperature

5. Software issues

  • Software glitches: sometimes, the EML may come on due to a software glitch in the vehicle's computer system. In such cases, try disconnecting the battery for a few minutes to reset the data. If the EML is still on, it’s best to get it checked out by a professional mechanic

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How serious is an Engine Management Light?

The seriousness of an Engine Management Light (EML) being on can vary depending on the specific issue causing it:

  • Minor issues (steady amber light): sometimes, the EML can be triggered by relatively minor issues like a loose fuel cap. In such cases, tightening the fuel cap might turn off the light and resolve the issue
  • Moderate issues (steady amber light): the EML could also indicate problems like a malfunctioning oxygen sensor or a failing mass airflow sensor. While these issues might not cause an immediate breakdown, they can impact a vehicle’s performance and fuel efficiency and should be addressed as soon as possible
  • Serious issues (red or flashing light): at times, the EML can indicate more serious issues like engine misfires, catalytic converter damage, or transmission problems. If the EML is flashing or blinking, it usually indicates a severe issue that requires immediate attention

Will my car pass an MOT with the Engine Management Light on?

No. If the EML is on during the MOT test, it will be classified as a major defect and will result in a failed MOT test.

If the EML is a steady amber, you can continue driving your vehicle to your closest destination. We strongly advise you to get the issue checked out by a professional mechanic as soon as possible.

If the EML is red or flashing, it indicates that there is a more serious problem and you should get this issue checked immediately.

When you’re booking your MOT in Caura, select ‘Repairs’ and let us know that the Engine Management Light needs to be checked before the test. The garage will make sure that this is repaired before the MOT test to avoid an MOT failure

How much does it cost to repair the Engine Management Light?

The cost of repairing the issue causing the EML to come on can vary significantly depending on the specific problem, make and model of your vehicle.

It's important to understand that the EML itself is not the component being repaired, but rather the light is an indicator of an underlying issue that needs to be addressed.

Here are some general cost estimates for common issues related to the EML*:

  • Oxygen sensor replacement: £100 - £300
  • Catalytic converter replacement: £300 - £1,000+
  • Mass airflow sensor replacement: £100 - £300
  • Ignition coil and spark plug replacement: £100 - £250
  • Fuel injector replacement: £100 - £500
  • Exhaust Gas Recirculation (EGR) valve replacement: £150 - £400

*It’s worth noting that these will vary by your location, the type of garage you go to, and what vehicle you have.

Ready to book an MOT, car service or repair?

Download Caura on the Apple App Store or Google Play Store and book with a vetted MOT garage near you. All you need to do is:

  • Enter your postcode
  • Pick a garage near you
  • Select the jobs you want done – you can pick more than one job, so if you need an MOT, car service and repair, go ahead and select all three
  • Confirm the dates you’re free

That’s it! We’ll let you know once the garage has confirmed the booking and for what date, and you’re all set.

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