i skiped to the end so someone may have said this but get one of those testers that plug into the connector under the dash on the dirver side by the door. and see if any codes come up. at the advanced auto stores around here they will do it for you for free. most likely there is a code in your computer and using one of those tools will tell your what is doing it so your can get it fixed. one time i unhooked the o2 sensor on our honda civic and pluged it back in and the check engine light came on, unhooked the batter for a few and hooked it back up and it went away.