Illumination of the Check Engine Light can be caused by a loose or worn gas cap.Google+
Car Problem Reports
Saturn L300 Check Engine Light Due to Gas Cap Issue
Saturn L300 Problem
Average Mileage: 100,166 mi (14,500 mi - 140,500 mi)
Visitor, 2004 Saturn L300, 131,000 mi
The check engine light came on and the repair shop replaced the gas cap. The light came on again and they checked the system with smoke. No leaks were found in the system but the light did not come back on.
The light now comes on and goes off intermittently.
Visitor, 2004 Saturn L300, 90,000 mi
Had the same problem and lived with it for 3 years; finally check engine light didn't turn off with new gas cap and needed to replace catalytic converter. Unrelated, have put in two water pumps one at 90M miles and this one at 148M miles. Still love my car and parts do fail. This has been a very reliable auto. Now I've learned I should have had my brake fluid flushed with the brake jobs...that's next on the maintenance schedule.
Visitor, 2004 Saturn L300, 140,500 mi
engine light comes and goes due to gas cap. replacing th cap resolved the issue for a few weeks then it reappeared.
Visitor, 2004 Saturn L300, 110,000 mi
engine light coming on. Change gas Cap and problem fixed.
Visitor, 2003 Saturn L300, 14,500 mi
everytime i put gas in my car approx 1/2 hr later my ck eng light comes on and my saturn dealer can't find the problem