I just fueled up my car, and as soon as I turned it on, I got a check engine light. It did not go away, so I consulted the manual. It said that a loosely closed gas cap could be the reason for a check engine light. Well I checked the gas cap, and it was not closed all the way. Now I need a way to clear the check engine light without a dealership that will charge $$$. A: If that was the problem, it will go away in a few days. It takes a couple of run cycles without the problem present before the light resets itself. But usually a loose fuel cap doesn't lead to an instant check engine light. So it is possible it's some other problem. If I were you I'd have your mechanic read the error code in memory to see what it really is. By the way, someone is bound to tell you just disconnect the battery. Please don't, unless you want further problems.