I have an 05 gxp and I got a check gas cap error the other day. I haven't put a new cap on, but I've checked everything on and around it and everything is clean and intact. Just looking for anything specific to look at. What exactly causes this error? If I need a new cap that is no problem, but is there anything else to check or do before I go buy one? I have taken the cap off and reseated it several times and reset the error but it just keeps coming back. Thanks for the help in advance.

*** Moved from Performance Area - Kevin ***

I've had this error thrown as well and ??? maybe I just didnt get it to "snap" they way it'* suppose to. Took it off, put it on, trouble warning gone.

Have also had low oil and antifreeze warnings without them being low.

I get the same problem and I did change my gas cap. I still get the error. I have noticed for quite a while if I fill my gas to the top I get a strong smell of gas and a few drops leak out. I've checked the rubber hose that connects the metal fuel input to the top of the gas tank and still the leak. Someone here mentioned a canister getting flooded but I really don't understand...

I'm not sure where the evap canister is, but that'* the only canister I can think of that when blocked or flooded can create that error. I don't have a GXP, but the canister is more than likely in the engine compartment.

part of the problem could be the venting of the cap. There is a vent tube that occasionally ets blocked or corrodes...causing the failed gas cap message. If you look under the car where the filler neck goes into the tank, at least if you can see any of it... The other problem is if the cap doesnt seat correctly it will cause the prompt, even after you smooth the tank neck and make sure there are no pitts in the neck of the filler tube....it will still take several tankfulls of fuel to clear the prompt, the computer requires before it resets (this from GM)....
I stuffed a rag in the neck, hand sanded to lip around the tank, then once I was certain it was smooth and the cap was in good shape, put a small bead of vaseline on the cap...then put it back on, 2 tankfulls and the light went out....