The most common cause for the P0440 code on a GM like yours is the vent valve solenoid that is mounted under the truck. This is the EVAP vent valve. It lets air into the fuel system as fuel is pumped into the tank. Plus it allows for the tank to equalize pressure. It looks like the picture and is mounted above the fuel tank on the cross member behind the fuel tank. If this is a 2 door or 4 door with an under body spare tire the vent will be above it.
The valve has a 2 pin wiring connector and the vent line has a quick connect on the end and it clips into the bracket on the frame.
The valve is really easy to replace if you are not in a rust belt area.
Images (Click to enlarge)
Tuesday, October 29th, 2019 AT 6:31 PM