Possible causes – Plugged vapor canister– Faulty vent solenoid– Pinched or blocked EVAP hose– Faulty FTP sensor Tech description Dirt and dust intrusion into the EVAP canister vent hose assembly, resulting in restricted air flow, may cause this condition. There is a bulletin for the following models:1999-2007 GMC Sierra (Classic) Models2007-2008 GMC Sierra Models GMC…