The short answer
Yes. An illuminated engine management light — also called the malfunction indicator lamp — is listed as a reason for failure in the MOT test for most petrol and diesel cars. The light must work and it must be off while the engine runs.
Why clearing the code the night before does not work
The tester checks the light itself, so a cleared code with a working bulb may pass the visual check — but the car's onboard readiness monitors need driving cycles to reset after a code clear. A diagnostic tester can also see that codes were recently erased, and the underlying fault frequently re-triggers the light within days. If the fault is still there, you have bought a short delay, not a pass.
What usually causes the light before an MOT
- Misfire history from coils or spark plugs
- Lambda (oxygen) sensor faults
- EGR and DPF faults on diesels
- Loose or perished fuel cap on petrol cars
- Wiring and connector faults
Get it read before test day
If your light is on and the MOT is coming up, book a diagnostic read first. You will know whether you are looking at a ten-minute fix or a repair — and you will not pay for an MOT that was always going to fail. Call 07440 140340 to book.