Illumination of the Check Engine Light can be caused by a loose or worn gas cap.Google+
Car Problem Reports
Saturn Ion Check Engine Light Due to Gas Cap Issue
Saturn Ion Problem
Average Mileage: 78,109 mi (34,000 mi - 147,000 mi)
Visitor, 2004 Saturn Ion, 90,000 mi
Check engine light was on. Got a new gas cap and light went off. Was told it was a vapor leak and could cost $400 to figure out the problem. Thankfully we decided to try the gas cap first. It worked!!
Visitor, 2006 Saturn Ion
My 2006 Saturn ION was showing an check engine light and when I took it to a Saturn dealership they were going to charge me $98 to hook it up and tell me what was wrong. Luckily, I had a friend who had the machine to do this and was able to tell me that it was the gas cap. About a week later the light came on again and since I had problems with the dealership and my oil change I had them check on the light for me and they also diagnosed it as the gas cap. This is twice in two weeks that this light has shown up. I hope this is the last time but I guess we'll have to wait and see.
Visitor, 2006 Saturn Ion, 59,700 mi
check engine light came on last night...my son - in -law pumped gas last and I always click my gas cap several times because I have had this problem before with another automobile....I am glad I read this article here today. I am praying this is all it is. Due mostly to the fact I just found out I need hearing aides and certainly cannot afford any car repairs at this time. Wish me luck I am trying the cap tonight:)
Visitor, 2005 Saturn Ion, 51,000 mi
the light comes on in the mornings have to play with gas cap
Yeah I have this problem also.
Visitor, 2005 Saturn Ion, 65,000 mi
At first I thought maybe someone was siphoning off my gas. Because about weekly, the light would be on, and I would check and the gas cap would be popped off.
Visitor, 2007 Saturn Ion, 59,500 mi
If the gas cap is not screwed on tight, the engine light comes on.
Visitor, 2007 Saturn Ion
Switched to a locking gas cap. Worked OK first few fillups. Once I left it loose and the light came on, it would not reset (several fillups, starts & stops) even after sc=ecuring it. Returned to old cap, light was out before the end of the next trip.