GM Repair Problems? Ask GM Repair Expert Now.
Hi and thank you for the question. My name is ***** ***** I'll do my best to help. A P0455 is a large Evaporative emissions system leak detected code, as you most likely know. The most common issue is the gas cap, which you replaced. The best way to have this properly diagnosed, is to have your local shop or dealer perform a "smoke" test on the Evap system. Has any other work been performed on the vehicle prior to the light coming on?
We couldn't connect unfortunately via a phone call, it just rang...would you like to try again?
Please accept my apologies, the previous message was to a different Denali customer...
Ok good to know. Have you checked any / all of the evaporative emissions lines on or around the engine to make sure one of the vacuum lines was not left disconnected?