Chevrolet Repair Questions? Ask a Mechanic for Answers ASAP
Welcome. This issue is because of the dirt and dust getting past the filter in the EVAP vent above the rear axle and has plugged the canister. What you need to do is replace the valve, clean the canister. The normal replacement valve will eventually let this happen again, but if you get the valve for the trucks it will allow you to run the filter using 5/8 heater hose under the hood away from the dirt and this will correct this.