Check engine light kept coming up for months indicating a P0446 error code. This refers to the Evaporative Emissions Vent System Performance. First we tried replacing the gas cap but about a week later the code came back up. We then took it in to a local shop and they cleaned out all of the hoses that are connected to the emissions system. Light came back on again. Eventually we took it to a GM mechanic and they found that the EVAP Canister Vent Solenoid/Valve was completely clogged with dirt and dust. The part should be hollow but when they removed it it had about 3 pounds of dirt in it. Upon replacing the canister the light went away and hasn't been back.

We found out that the hose that is connected to this part is run along the bottom of the truck and comes out where the rear driver side wheel well is. You'll literally see this hanging there if you look under the vehicle and up to where the hose from the gas tank meets the gas cap. It just dangles there with a small filter on the end. So if you travel on dirt roads regularly the wheels kick up dust and it goes right into this hose and gets sucked into the canister. After replacing the canister we rerouted the hose to under the engine so that it no longer sucks in dirty air from the wheel well. This should solve the problem permanently.