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Home >> GMC >> 2006 >> Sierra 1500 HD, RWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 942 (Engine Controls And Fuel - 6.6L (LMM) - DTC P154B To DTC P2693) >> DTC P2636 >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different car, the 2007 GMC Sierra, 2007 GMC Cab & Chassis Sierra, 2007 Chevrolet Silverado, and 2007 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
IMPORTANT:
  • You must perform the Circuit/System Verification before proceeding with Circuit/System Testing.
  • If the fuel level is not between 25-50 percent, add 19 L (5 gal) in order to perform this diagnostic procedure. If the fuel level is not within this range, misdiagnosis will occur.
  1. Turn ON the ignition, with the engine OFF.
  2. Command the fuel pump relay ON and OFF with a scan tool. You should either hear or feel the fuel pump relay click with each command.
    • If the fuel pump relay did not clicked when commanded ON and OFF, replace the fuel pump relay.
  3. Remove the fuel pump relay from the underhood electrical center.
  4. Probe the positive voltage supply circuit of the fuel pump relay with a test lamp that is connected to a ground. The test lamp should illuminate.
    • If the test lamp did not illuminate, test the positive voltage supply circuit for an open.
  5. Connect a fused jumper wire between the positive voltage supply circuit of the fuel pump relay and the voltage supply circuit of the fuel pump. The fuel pump should operate.
    • If the fuel pump did not operate, test the voltage supply circuit of the fuel pump and the ground circuit of the fuel pump for an open.
    • If the positive voltage supply circuit fuse opens, test the voltage supply circuit of the fuel pump for a short to ground.
    • If all circuits tested normal, replace the fuel pump.
  6. With the fused jumper still connected, observed the Fuel Level sensor voltage parameter with a scan tool. The rear fuel level voltage should increase as the pump is operating.
    • If the fuel level voltage did not increased, inspect the fuel lines and the fuel sender for a restriction at the rear fuel tank.
  7. Remove the fused jumper and disconnect the outlet hose from the fuel pump. Connect a section of rubber hose with a clamp to the outlet port of the fuel pump. Insert the other end of the hose into an approved container to measure more than 4 liters (1.06 gallons) of fuel. Operate the fuel pump for a total of 2 minutes and measure the fuel in the container. There should be 2.6 liters (0.70 gallons) of fuel.
    • If the fuel volume did not measure more than 2.6 liters (0.70 gallons) within the specified time, replace the fuel pump.
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