Illumination of the Check Engine Light can be caused by a loose or worn gas cap.
Car Problem Reports
Saturn SC2 Check Engine Light Due to Gas Cap Issue
Saturn SC2 Problem
Average Mileage: 79,500 mi (60,000 mi - 99,000 mi)
Visitor, 2001 Saturn SC2
I had the check engine light on in my car, so I took it in to get a diagnostic. The mechanic explained that the car is designed to recycle gas vapors, and if some of those vapors escape through the gas cap, then the car detects that as a leak, and the check engine light goes on. He put a new gas cap on the car and the light's been gone since.