Illumination of the Check Engine Light can be caused by a loose or worn gas cap.Google+
Car Problem Reports
GMC Yukon Check Engine Light Due to Gas Cap Issue
GMC Yukon Problem
Average Mileage: 118,142 mi (60,000 mi - 280,000 mi)
Visitor, 2007 GMC Yukon, 102,000 mi
same problem changing the cap tomorrow
Visitor, 2007 GMC Yukon, 75,000 mi
Same issue with my yukon, light is on and I replaced gas cap. Check engine light is still on
Visitor, 2004 GMC Yukon, 280,000 mi
tighten fuel cap notification comes on - and then goes off.
haven't replaced cap yet
now have check engine light...
Visitor, 2007 GMC Yukon
My check engine light comes on frequently and when i push the onstar button for them to run a diagnostic check they say it is an emissions problem and to take it in if the light does not turn off 7 more times after running your vehicle. This becomes annoying when you take it to the dealer and they want to charge you for checking out the vehicle and just say they needed to replace the gas cap, and then the light is reset, then a month or two later the light turns on again and it is the same issue, instead of just replacing the cap fix the real problem and stop charging people to make money!