Check engine light, bad gas cap

[piecesparts]

Had to get a new gas cap. The original cap was not sealing properly and the check engine light kept setting on an intermittent basis.

[POPSG8GT]

I have had two incidents of this problem. One just today...I checked the gas cap and it was loose!!!! I know I put it on tight...why or how does it get loose???? My check engine light came on and I immediately checked the gas cap and it was loose. I don't understand this...anyone else have this problem?
Thanks,
POPSG8GT

[WickedMom]

Make sure you are not pushing on the cap when you are tightening it... just twist and make sure it clicks a bunch

[Panzer Leader]

Had same problem. Happened once. Dealer said if it happens again then the cap would be replaced. In the meantime, I followed the advice on the forum. Take a little vasoline jelly or other type (in our sorry cases, perhaps KY) and coat the seal on the cap.

[piecesparts]

Had same problem. Happened once. Dealer said if it happens again then the cap would be replaced. In the meantime, I followed the advice on the forum. Take a little vasoline jelly or other type (in our sorry cases, perhaps KY) and coat the seal on the cap.

keep in mind, the cap has a small spring loaded vent in the middle, too.

[POPSG8GT]

Had our G8 GT in for the check engine light today (plus vibration around 60-70 mph).
They ordered a new gas cap (seems as though there is a shortage of these...I wonder why??? Ha!!).
They did a "load balance" on the wheels and determined the left front was out. I took it for a short drive to see if the balance problem was fixed and it seems as though it worked. We will see once I get it on the Interstate.

[WildBill]

My gas cap broke the other day, the "guts" (the threads and check valve, etc) all came off the "handle" assembly. My dealer should have a new one for me tomorrow, I hope. I've got it hacked together at the moment, car hasn't thrown a code so I think it's working. :)

[Kermit]

Glad to see others have been having this problem. My gas cap has worked loose at least 7-8 times now. Looks like I will have to let the dealership know about this problem when I go to get my Recall done.

[BlutoRS]

My cap was loose too. I knew I wasn't crazy! Same issue here guys.

[SSD]

Mine got replaced as well, never noticed it getting loose, though.

[POPSG8GT]

The dealer got rid of my vibration...they "load balanced" the tires. Found one out 1/4 oz. That don't sound like much, but the vibration is gone. Also, they installed the new gas cap (on Saturday no less).

[WickedMom]

Glad the vibration is gone, $10 says it comes back at your next rotation.

[POPSG8GT]

Hope not....I won't be happy if it does....and that is not good!!!

[WickedMom]

I actually got a check engine light today. P0455 Large evap leak, my tech TRIED to tell me it was my cap or that someone was messing with me. He didnt know that the gas door locks when the doors are locked :) I know my cap was on right.

[Larry GT]

How embarrassing! Mine shattered at the gas pump, (in front of way too many people).

I thought I placed the pieces back together, but the check engine light said otherwise. The dealer replaced the cap gratis, though it took 24 hrs. to get one from Salt Lake.


The new one does look different, and I now very gingerly handle the replacement cap.

[Panzer Leader]

Second incident today. Called OnStar they said that it was probably the problem . Headed by dealer, they ordered the new cap. (Isn't there not a redesigned cap?) Also said they would have to do a "smoke test???" to make sure there is not another leak. Well OK if you must. Guess the warranty dollars are flowing. Second time is a charm I guess. BTW had OnStar connect me with GM Corp Customer Service. I spoke with them on this and other issues. Especially the front ball joint problem. I also asked to be transfered to bob lutz's office, but he is not accepting calls from G8 owners.

[-Ray-]

My cap hasn't done this. Why redesign it?
Perhaps China had a bad batch.

[Panzer Leader]

I think there are other threads on this issue. I thought someone said there was another cap out with a different part number. Anyway the cap lasted to over 10k miles, ball joints maybe 10k miles, driveshaft to 10K. I guess I will rename it the G10. I really love this car, so much potential.

[POPSG8GT]

Update....No check engine lights have returned as of today...plus vibration is not present. So far I am a happy camper.

[piecesparts]

So far I have gone all the way to a complete new gas tank and fittings on the connections. I haven't had any issue as of late.

[KansasG8]

This happened to me on a trip. The Check engine light came on and freaked me out. Onstar told me to check the fuel cap, it was loose. haven't had a problem since though, that was the first of sept.

[roSSco]

The rubber seal in mine was way too small for the top of the tube. Got a new one and all is well.

[bigtreepu]

This happens to me every few months. When I get a CEL, I check the gas cap. Not sure what I'm gonna do when it's not that! Get out the reader I guess. So is it confirmed there is a new gas cap available from dealers? If so I'm gonna go pick 1 up.

~Matt

[mrj88]

mine has done this 4 times

[WickedMom]

There is a slightly updated cap that was released... the cause from what I have heard has to do with the caps prematurely clicking before they are really secured.

If you cap clicks too quickly, start over.

[piecesparts]

The dealer that I had my fuel tank replaced at, said he has had a couple more G8s with the same problem. It is not always the gas cap, some of the tanks have a bad connection on them and there is a small leak at a point where a vent line is connected to the tank. It is on top, out of sight and is hard to find. I have not had a CEL since we changed out my tank.

[WickedMom]

We have replaced 3 tanks at my store, two returned with repeat CELs.