The fuel pump module on a GMC truck is installed directly within the fuel tank. Like many of its type, removing and replacing a defective fuel pump means removing the tank from the truck itself first. In most cases, you need to replace the entire pump module. You can switch the fuel sensor unit to a new module on some newer models.
Disconnect the truck's negative battery cable.
Unscrew and remove the cap for the fuel pressure test port, which is usually located on the right side fuel rail. Wrap shop rags around the port and then relieve the pressure by pressing on the valve in the port with a small screwdriver.
Raise the truck's rear end using a floor jack and support it on jack stands. Remove the bolts for the tank's rock guard using a wrench and remove the guard.
Loosen the hose clamp screws for the tank's filler neck hose and vent hose with a screwdriver and disconnect the hoses from the tank. Disconnect the tank's EVAP line at the EVAP canister, then disconnect the fuel supply line at its quick-connect fitting.
Unbolt the fuel tank straps with the wrench while another person supports the tank. Lower the tank until you can reach the electrical connectors to the fuel pump module, then disconnect them and remove the tank.
Grasp one end of the fuel pump retaining ring with locking pump pliers and turn it counterclockwise to unscrew and remove it. Tap the ring with a hammer and brass punch--not a steel one--if the ring needs help loosening,
Draw alignment marks with a marker on both the pump's mounting flange and the fuel tank. Use the pump's alignment mark as a guide to draw a mark on the replacement pump module.
Lift the fuel pump module out of the tank until you can reach the quick-connect fitting for the ventilation harness. Disconnect this fitting and remove the module.
Pull off the O-ring surrounding the mounting hole in the tank and inspect it. Replace the ring if it is cracked or deteriorated in any way.
Lower the replacement fuel pump down into the fuel tank using the alignment marks to position it. Tilt the module at an angle as you insert it so you don't damage the float arm.
Screw the locking ring in place and tighten it down using the water pump pliers or the punch and hammer.
Connect the fuel supply and vent lines and the electrical connectors to the fuel pump mounting flange using their quick-connect fittings.
Raise the fuel tank into position on the truck with your assistant's help and secure the tank with the straps, bolting them in place with your wrench.
Connect the filler and vent hoses to the tank using their hose clamps and your screwdriver. Connect all other supply and EVAP lines using the quick-connect fittings.
Bolt the rock guard back over the tank with the wrench, then lower the truck off the jack stands and reconnect the battery cable.
