Illumination of the Check Engine Light can be caused by a loose or worn gas cap.Google+
Car Problem Reports
Chevrolet Avalanche Check Engine Light Due to Gas Cap Issue
Chevrolet Avalanche Problem
Average Mileage: 77,666 mi (46,000 mi - 110,000 mi)
Visitor, 2007 Chevrolet Avalanche
this is a constant issue. we have even tried purchasing new gas caps but the issue still happens.
Visitor, 2007 Chevrolet Avalanche, 55,000 mi
gas cap loose wont tighten check engine light comes on
Visitor, 2009 Chevrolet Avalanche, 46,000 mi
Back in December, I had my engine light go on. Had the problem checked and I was told that there is a loose or faulty gas cap. Have not replaced gas cap yet.