A Loose or worn gas cap may cause Check Engine Light to illuminate.Google+
Car Problem Reports
GMC Yukon Denali Check Engine Light Due to Gas Cap Issue
GMC Yukon Denali Problem
Visitor, 2007 GMC Yukon Denali
Got a diagnosis with a code using the code machine...the code could have been a couple things related to gas, but it was determined that it was just that the gas cap was too loose ....just replace the cap.