A Loose or worn gas cap may cause Check Engine Light to illuminate.Google+
Car Problem Reports
GMC Jimmy Check Engine Light Due to Gas Cap Issue
GMC Jimmy Problem
Average Mileage: 168,400 mi (109,000 mi - 220,000 mi)
Whenever I get gas, I tighten it to about 5-6 clicks, the check engine light comes on. I have had this checked and its my gas cap. I need to get another one to see if this stops the light from coming on. I can't get my vehicle inspected with this light on. But I am sure getting a new cap will fix this problem.