My car has had a few engine check lights come up over the last couple of weeks and they have eventually gone of their own free will. I think it was a cold start missfire alarm, which has sort of cured itself at least at the moment. But I think that the error code is still stored even if the light has gone. I have checked with a universal code reader when the light has gone but can find no codes, I think I need someone with a BMW specific reader to find them