check engine light on 2004 Chevrolet Colorado

My check engine light comes on and stays on even when the truck is turned off. Overnight it drains my battery and i have to jump it to get it running. Any idea as to what is causing this?

Asked by for the 2004 Chevrolet Colorado
I had it happen in mine too because of the gas cap. To reset the check engine light, as soon as you turn the key,pump the brakes hard 3 times. That fixed mine. Though it always reappears.
3 answers
It sounds like your Ignition switch is defective and not completely turning off.

here is some info about the light when it is on while driving

http://repairpal.com/check-engine-light
your alternator might be shorted out internally. try taking it out and having it tested. my truck had the same problems. i also had problems with power locks and windows when the battery went dead