Illumination of the Check Engine Light can be caused by a loose or worn gas cap.Google+
Car Problem Reports
GMC Sierra Denali Check Engine Light Due to Gas Cap Issue
GMC Sierra Denali Problem
Average Mileage: 110,500 mi (86,500 mi - 135,000 mi)
Visitor, 2006 GMC Sierra Denali, 110,000 mi
check engine light comes on. tighten gas cap and goes off for awhile. replaced gas cap but still happens.