I have a service engine light on my 2008 Chevy Impala I have replaced the gas cap and the battery. I have had this car since 1/2009 and this has been going on for 2 or 3 weeks now.
Something drained my battery and when I started it again it sounded like a pump running in the front of the car finally got it to stop when I got the gas cap to stay on so replaced gas cap, light came back replaced bettery cleared codes and the light came back.
I am a mechanic by trade