Does the engine management light on fail an mot test?

Yes, an illuminated engine management light will result in a failed MOT test. The engine management light is designed to alert the driver to potential problems with the vehicle's engine or emissions control system, and as such is considered a major defect. If the light is illuminated during the MOT test, the vehicle will fail the test and will not be issued a valid MOT certificate until the problem has been rectified and the light is no longer illuminated.