The engine malfunction indicator lamp, the MIL, is also called the engine management light or EML. At MOT it produces one of the most-looked-up defect wordings there is: Engine MIL inoperative or indicating a malfunction.
It is a Major defect, which means a fail. But it only applies to vehicles that are required to have a MIL in the first place, and that is where most of the confusion sits.
Everything here comes from section 8 of the DVSA MOT inspection manual, checked 2 August 2026. It is a companion to the manual, not a substitute for it.
How the check is done
Turn on the ignition and check that the MIL illuminates and then goes off. On some vehicles you will need to start the engine before it goes off.
That is the whole check, and it catches both failure modes in the defect wording: a lamp that never lights is inoperative, and a lamp that lights and stays on is indicating a malfunction. Both are Major.
Which vehicles must have a MIL
The requirement depends on fuel type, wheels, passenger seats and date of first use.
Petrol, including hybrids
- 4 or more wheels, not more than 8 passenger seats in addition to the driver, first used on or after 1 July 2003.
- 4 or more wheels, more than 8 passenger seats in addition to the driver, first used on or after 1 July 2008.
Gas and bi-fuel, including hybrids
- 4 or more wheels, not more than 8 passenger seats in addition to the driver, first used on or after 1 July 2008.
Diesel, including hybrids
- 4 or more wheels, first used on or after 1 July 2008.
Which vehicles are not required to have one
Kit cars, amateur built vehicles and American pickups are not required to be fitted with an engine MIL. If there is no requirement, there is no defect to record.
Where it sits in the manual
The MIL check appears twice, once for each engine type, and the defect is Major in both places:
- Petrol: section 8.2.1.2, gaseous emissions. Defect (h).
- Diesel: section 8.2.2.2, opacity. Defect (g).
The conversation at the counter
This is one of the failures customers argue about, because the car drives perfectly well with the light on. The useful framing is that the MOT is not asking whether the car feels right. It is asking whether the vehicle's own diagnostic system is reporting a fault, and whether the lamp that reports it works at all.
A lamp that has been removed, taped over or bulb-pulled is still inoperative, and still a Major defect.
Read the section properly
Section 8 also covers exhaust noise, emissions limits for petrol and diesel, opacity testing and fluid leaks. If you are looking up the MIL rules you will probably want the rest of it too. Open section 8 on GOV.UK, or start with our map of the whole manual.