Had the 'engine management light' on in my Avensis for 3 years. Checked at garage when it first appeared and nothing wrong (glitch somewhere? ) so they cleared it, said if it comes back we'll look further . . . ££££ . .
It came back on 2 months before it's MOT . . I reset it . . flew through the MOT (emissions etc) and after that I just kept resetting it occasionally.
There were absolutely zero engine problems in those 3 years . . apart from a new starter motor . . bloody modern cars eh