[cobrajeff]

I've had this happen on both my Miata and my Mountaineer. When my girlfriend puts gas in, she doesn't get put the gas cap back on tight enough. The computer is so sensitive, it detects this, and turns on the "Check Engine" light. A battery disconnect for about thirty seconds will usually reset it back to normal (check & tighten gas cap FIRST).

I found this trick on a Miata forum, and it worked for me. When it happened on my Mountaineer, I forgot she had driven it, so I figured it really must have an issue. My friendly Mercury dealer only charged me $37 to test it and tell me "the gas cap was probably loose".

Live and learn, I guess....

Jeff