I've been fighting the infamous CEL (Check Engine Light) since buying my 1998 Wrangler, with some success until recently. I used a friends nifty reader to find the related code is "PO442 EVAP Emission Leak (Small)".
There are some interesting symptoms related to the CEL; it comes on only when my fuel level falls below quarter tank, and may (emphasis on the may) go off after a couple of refills as long as I never let it drop below quarter full. I also over-filled the tank one time and gas came out from the top of the tank, and not from the filler (freaked out the lady next to me :o )
Where should I start looking to fix the leak? Internet research shows it could be as simple as the gas cap, or as time consuming as the o-ring on the fuel pump.