I have a 2004 TJ I recently purchased. There were plenty of minor things to do, and it seems like I am at the final steps of finally finishing all the mechanical issues. My check engine light is on (has been on since i bought the car). I have been doing a lot of research and know where i am supposed to look, but i just cant find anything that seems out of the ordinary on mine. Everything seems ok, and the vaccum lines and connections all seem to be in place. I read that it might be the gas cap? It does not look like it is the original one, Looks like an aftermarket one I have seen at a local autozone. Please tell me where to look or let me know how you would troubleshoot the problem if it were your jeep. I appreciate all of the help i get. Thank you!