Fuel Pump Electrical Circuit Diagnosis
CIRCUIT DESCRIPTIONWhen the ignition switch is turned ON, the control module energizes the fuel pump relay which applies power to the in-tank fuel pump. The fuel pump relay will remain on as long as the engine is running or cranking and the control module is receiving crankshaft position (CKP) sensor reference pulses. If no CKP sensor reference pulses are present, the control module de-energizes the fuel pump relay within 2 seconds after the ignition is turned ON or the engine is stopped. The PCM applies a low current signal of approximately 7 volts to the fuel pump relay control circuit with the key ON and the engine OFF. The PCM uses this signal to detect the integrity of the fuel pump relay control circuit.
DIAGNOSTIC AIDS
Diagnostic Aids:
TEST DESCRIPTION
Steps 1-6:
Steps 7-9:
Steps 10-13:
Steps 14-17:
Steps 18-23:
Steps 24-26:
The numbers below refer to the step numbers on the diagnostic table:
2. Command both the ON and OFF states. Repeat the commands as necessary. This can be determined by listening for an audible hiss from the fuel pump when the fuel pump relay is commanded ON or a vibration in the fuel feed line.
3. This step determines if the condition is located on the coil side or the switch side of the relay.
5. This step determines if the fuel pump relay is stuck closed.
7. This step tests for a grounded voltage supply circuit. The fuel pump fuse supplies power to fuel pump. Disconnecting the fuel pump in-line harness connector isolates the fuel pump voltage supply circuit.
9. This step verifies that the ECM is providing voltage to the fuel pump relay.
10. This step verifies that the fuel pump fuse is providing voltage to the fuel pump relay.
11. This step tests for an open circuit or a short to ground causing an open MaxiFuse.
12. This step bypasses the fuel pump relay in order to activate the fuel pump.
13. This step tests for an open in the fuel pump feed circuit between the in-line connector and the fuel pump relay.
16. This step tests for an open or high resistance in the fuel pump ground circuit.
18. This step determines if the condition with the circuit is intermittent. If the fuse does not open, inspect the supply voltage circuit between the fuse and the fuel pump for an intermittent condition.