Illumination of the Check Engine Light can be caused by a loose or worn gas cap.
Yukon XL 1500
Average mileage: 118,891 (99,000–160,000)
19 people reported this problem
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GOT A NEW CAP FOR GAS TANK, ISSUE REMAINS
LOOSE GAS CAP LIGHT COMES ON OFTEN, I CHECK IT AND IT'S TIGHT, SO FIGURE THAT THE GAS CAP IN JUST WORN.
Never fixed. Light stays on. I just ignore it.
Engine light code indicated loose gas cap - replace. I have replaced it 3 times parts store caps and oem caps. Still get light about every 6 months. When I open gas cap, gas tank is pressurized!