Circuit/System Testing

With the ignition OFF, remove the fuel pump relay from the rear electrical center.
Test for less than 5 ohms of resistance between the ground circuit and ground.
- If greater than the specified range, test the ground circuit for an open/high resistance.
Connect a test lamp between the control circuit of the fuel pump relay and the ground circuit. Command the fuel pump relay ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.
- If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the engine control module (ECM).
- If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the ECM.
Inspect the fuel pump fuse.
- If the fuel pump fuse is open, test for the following conditions:
  - A short to ground in the supply voltage circuit of the fuel pump
  - A short to ground in the relay switch B+ circuit
    - If the above circuits test normal, replace the fuel sender.
Verify that a test lamp illuminates between the B+ circuit and ground. If the test lamp does not illuminate, test the B+ circuit for an open/high resistance.
- If the test lamp does not illuminate, repair the open in the battery positive voltage circuit.
Connect a 15A fused jumper wire between the B+ circuit and the supply voltage circuit of the fuel pump. Verify the fuel pump is activated.
- If the fuel pump does not activate, test for the following conditions:
  - An open/high resistance in the supply voltage circuit of the fuel pump
  - An open/high resistance in the ground circuit of the fuel pump
    - If the above circuits test normal, replace the fuel sender assembly.
If all circuits test normal, test or replace the fuel pump relay.