Got my 09 G8 GT on 9-5-08 since then the "check engine" light has come on twice. I took it to the dealership and had it put on the computer-both times the light came on because the gas cap was loose. When I fill up, I tighten the cap myself(3 turns of "clicking") to ensure the cap is tight. It seems that, through normal driving conditions, the cap comes loose. Anybody else come across this problem? Thanks for the input.

I'm on my second check engine light on a 2008 G8 with just under 600 miles. The first check engine light came on at just under 500 miles and they said that was a loose gas cap. When I checked the gas cap this time, it seemed like it could have been loose because it turned a little before clicking. I also made sure it was tight after fueling up and you may be right about it loosening on its own maybe from vibration. I'll let you know what they say this time.

Gas cap for sure! After tightening the gas cap, the check engine light went off after driving a few miles. Called the service manager who said the retaining strap may cause the gas cap to come loose. Option to remove retaining strap or try a new gas cap. If it happens again, I'm going to have them order me a cap. Also the engine will start running a little rough when the cap is loose. That should be your indication to check the cap first if you get a check engine.

Most Domestic cars have the feature that if the gas cap us loose, the Service Engine Soon light comes on. Seems kind of wierd that the cap is coming loose while driving. Must be something wrong with the cap itself.

I've had the same problem with the gas cap. I seem to have solved the problem by keeping the strap on the bottom of the gas cap. This has happened to me three times before I figured it out.

i had the problem with my 08 and i narrowed it down to 2 things before it was werecked. it was either the extreme heat and i filled it during the day and also the way the strap was placed. i never got to play with neither enough since i really didnt have time to but the dealer never figured it out...

i just filled up for the first time, that cap is one cheesy piece of crap. no wonder people have had problems. i guess just make sure the strap is out of the way, and the seal is still good, then make sure you get a few good clicks out of it.

Good morning, i am so glad to have found this post and hope this is my only problem...my check engine light has come on 2x now...onstar suggested it could be the fuel cap or bad gas (i dont think its bad gas, it runs fine).

Has anyone replaced the gas cap yet and if so, did this solve the problem?

Thanks,
Sandra :)

I have the 2008 G8 and the Check engine light comes on quite a bit. If I get gas, while the car is running, the light will go off almost like clock work the next time the car is started. I have also noticed after getting on it hard, the light will come on shortly after, if, when the car is running I take the cap off then put it back on, I get the same result. The dealer has already replaced the cap, I noticed when the car was run semi hard for a 45 minute stent the back seat smelled a little like gas. That got me worried but it only happened the one time. I, as you may have figured out, am trying to troubleshoot the issue before bringing it back to the dealer cause telling me its the gas cap again will not be acceptable. Anyone got any new ideas or is it really just a crappy gas cap and can be solved with the placement of the strap, or the removal of it...

I am really long winded... sorry bout that...!

If the check engine light is coming on then what code is being thrown. tell the dealer you want it fixed not just a band-aid fixed.