So I have a 2018 Traverse LT FW with 36700 miles on it. Last week my check engine light came one. So I have a OBD reader on my sprint drive, and it alerted me that my P code was P0469 bad purge valve. So I change the purge valve, then this morning the check light came back on. Now its P0455 EVAP system leak detected (large leak). So there is no gas cap, so that went out the window. The only other choice I could think of is a bad vent valve. Any one have any suggestions, or have a clue where the **** the vent valve is located. I crawled under the vehicle and couldn't locate it, unless its on top of the gas tank.