Chris:

When I took the car to the dealer, the mechanic said that the cap was screwed on at an angle. The cap will still click when closed incorrectly this way. My wife and I were both relying on listening for the clicking sound after the gas station attendant secured the cap, not thinking that the cap could be screwed in incorrectly.

So now I'm closing the fuel cap myself, making the sure that I can feel the cap threading in before the thing clicks shut. I hope you can find out what the problem is with your check engine light. Thanks for taking the time to reply.

John