Hello, and welcome to JA!! you probably have a code P0446 or a P0449 stored in the system. this code and with the problem you are having, the vent sol. is stuck closed. this vent opens to allow the fuel tank to vent excessive pressures in the tank.. this is done so you can add fuel to the tank. on your vehicle there is a updated vent sol. that will be needed to replace to fix your problem. your dealer should be able to correct this under your factory warranty.
Please let me know if you need any further info on this concern.
rerouting is the correct way to fix. i have posted the info from gm on how to repair.
#02-06-04-037D: DTC P0446 (Restricted/Blocked Evap Vent Path) Set, Check Engine Light On (Replace Evaporative Emission (EVAP) Vent Valve Solenoid Assembly and Add/Relocate Filter Box Using Service Kit) - (Apr 16, 2008)
Some customers whose vehicles are operated in dusty type environments, such as farming or mining off-road type applications, may comment about the illumination of the check engine light, with a DTC of P0446 (Restricted/Blocked EVAP Vent Path) being set.
Dirt and dust intrusion into the EVAP canister vent hose assembly, resulting in restricted air flow, may cause this condition.
Correction (1999-2007 Classic/Old Style Models)
After following the published SI diagnostics for P0446 and determining that the EVAP canister vent valve is the cause of the MIL light, replace the existing EVAP canister vent valve assembly with a new assembly. This new assembly is a sealed unit that is designed to be vented through a remote filter box. To ensure correct installation, follow the procedures below.
Important: The new canister vent valve will be installed in a new location, outside of the frame.
Tighten Tighten the bracket mounting bolt to 12 N·m (106 lb in).
Correction (2007-2008 New Style Models)
After following the published SI diagnostics for P0446 and determining that the EVAP canister vent valve is the cause of the MIL light, replace the EVAP canister vent valve assembly and relocate the remote filter box. To ensure correct installation, follow the procedures below.
19152345 (1999-2003 Model Year)
Solenoid Kit, EVAP Emission Canister Vent Valve
19152349 (2004-2008 Model Year)
Cut to Length