Illumination of the Check Engine Light can be caused by a loose or worn gas cap.Google+
Car Problem Reports
Chevrolet Tahoe Check Engine Light Due to Gas Cap Issue
Chevrolet Tahoe Problem
Average Mileage: 80,333 mi (16,000 mi - 150,000 mi)
Visitor, 2007 Chevrolet Tahoe, 150,000 mi
Check engine light came on gave a code that there was a minor emission system leak.
Visitor, 2007 Chevrolet Tahoe, 16,000 mi
I repeated had the check engine light come on after I bought my truck (used w/ 16000mi). This took 8 trips to the dealer before they figured out it was a fuel line issue. The metal receiver for the gas cap wouldn't secure properly. Since it was a used car when I bought it I couldn't do the normal lemon law suit. I was able to sue for breach of contract and had GM award me money for the time & effort of 8 trips to the dealer and missed work hours.