Illumination of the Check Engine Light can be caused by a loose or worn gas cap.
2009 GMC Yukon XL Denali Problem Reports
Newest 2009 GMC Yukon XL Denali Problem Reports
One or more heater & AC (HVAC) temperature and/or air delivery mode door actuator may fail, resulting in improper temperature or air delivery. If this occurs, fault code(s) should be stored in the HVAC control module which should assist in diagnoses.