I just picked up my Devillefrom oil change , coolant change and complete brake job. As soon as I started it I noticed the check gas cap and Check engine lights are on. This happened to my moms 07 Focus, on hers I just twisted the gas cap and it all went off in two minutes. On my caddy the lights arent going off.

 

It may take a few ignition cycles but just go into the DIC and clear the codes, it will go out once you do that.

 

Thats what i did. it went away. Thanks Katzmans

 

 

I had the same trouble with my '99 Deville. I replaced the gas cap with one from the auto parts store - it fit, but it never seemed to seal well. I figured I would just live with the unending light show and reset the warnings every so often. That didn't last too long - I ended up buying a new cap from the dealer. The "check gas cap" and SES warnings seem to have gone away. I hope they do not come back. I read somewhere that this problem could cause the car to get lower gas mileage. After I put the dealer cap on the car, my mileage did improve from 22 to 24.5.