Why won't Truck allow gas through filler neck?

Hello, when this happens, there is likely an issue with fuel tank venting. This would be in conjunction with the evaporative emission system. Troubleshooting by a local shop near you is needed. www.repairpal.com/repair-shops

Yes it is an evap issue without a doubt. The *canister vent valve* is what’s causing this problem - that’s also without a doubt! I’ve fixed a parking lot full of em - it is a very common failure.