Illumination of the Check Engine Light can be caused by a loose or worn gas cap.Google+
Car Problem Reports
Pontiac Aztek Check Engine Light Due to Gas Cap Issue
Pontiac Aztek Problem
Average Mileage: 86,793 mi (54,000 mi - 147,000 mi)
Visitor, 2005 Pontiac Aztek, 80,053 mi
Lost my gas cap and had to replace it with a generic one that doesn't fit as well as it should. It was fine for about 1000 miles... but as soon as I hit 80,000 on the odometer the Check Engine Soon light came on.
Visitor, 2004 Pontiac Aztek
It happened twice because I didn't turn the cap until it clicked. After fixing the light went off, although 1 time it stayed on. Fixed by removing cap and driving a few miles and put it back on and light is off
Visitor, 2001 Pontiac Aztek, 85,000 mi
Comes on, old cap would not tighten brought a new one, same problem...cap is still loose
check engine light always on. I had mechanic reset it but it came back on after a week.
My gas cap completely broke off, I still have one inner piece I use to cover the gas tank so it is not left open to the elements but people always asked me why there was no cover for the gas cap. I hadn't even noticed when I bought my vehicle.
Visitor, 2001 Pontiac Aztek
No a problem, used On Star to check it. Since the '01 had an analog OS, I just tighten the cap again. Still happens occasionally with 122,070 miles. Love this vehicle!
Visitor, 2004 Pontiac Aztek, 54,000 mi
Check engine light on after replacing the worn gas cap with generic but nicely fitting cap.
Visitor, 2005 Pontiac Aztek, 97,000 mi
Service Engine Soon Light is on for the second time. I had it reset at a auto parts store
and yet after three weeks its on again.