My check engine light came on with a msg re fuel cap being loose, but it wasn't.

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My check engine light came on today with a message about the fuel cap being loose- I turned off the car, unscrewed it, retightened... it was definitely on tight enough. This happened about a year ago and after I did this, the light went away. This time the light did not go away. I also just had a major service done on my car in August. Wondering if it will go away on its own, if my car is safe to drive... I really can't afford a major problem right now.