Now after I have fixed all my issues with my new car I get a TIGHTEN GAS CAP message in the message center. Of course I got out and tightened it, shut the car down restarted it etc. I have now gone through 4 full tanks of gas and run almost to E without running out and the message continues to come on. Any suggestions?

 

Either the evaporative emissions system has a leak in it (could be a bad gas cap or a number of vacuum lines), the diagnostic pump is bad, or it hasn't re-run it's diagnostic check on the evap system to determine if there is a leak. It may also be a software problem, if GM is using software. I'm not sure what the requirements are for it to run the test, but I would think it would have run sometime within the last four tankfulls of gas.