Illumination of the Check Engine Light can be caused by a loose or worn gas cap.Google+
Car Problem Reports
Pontiac Sunfire Check Engine Light Due to Gas Cap Issue
Pontiac Sunfire Problem
Average Mileage: 102,564 mi (30,000 mi - 205,000 mi)
Visitor, 2003 Pontiac Sunfire, 53,000 mi
Engine light came on. Turned out the cause was the gas cap not being securely tightened. You have to hear clicks to be sure it's tight. My cap was very dirty. Cleaned it and it was fine but soon replaced it.
Visitor, 2003 Pontiac Sunfire, 128,000 mi
check engine light on but says evap code
I can always tell when someone other than myself has messed with the gas tank lid....either its coiled up all wrong or i ge the check engine light...I then make sure during my next stop to undo the cap and retighten it, making sure it clicks at least 2-3 times. Usually, the check engine light will then go off after a couple of restars after the cap has been retightened.
My check engine light was on so i went to mechanic and it was diagnosed as it being the gas cap. replaced gas cap-problem solved! ;)
Visitor, 1997 Pontiac Sunfire, 30,000 mi
Purchased new gas cap.