P0628
P0628-LOW VOLTAGE DETECTED AT THE FUEL LIFT PUMPP0628 - Low Voltage Detected At The Fuel Lift Pump:
WHEN MONITORED
While the key is on.
SET CONDITION
The commanded signal to the fuel lift pump relay does not match the feedback signal from the fuel lift pump relay.
POSSIBLE CAUSES
- Wiring harness
- Fuel lift pump relay
- Fuel lift pump relay driver circuit shorted to external voltage
- Fuel lift pump relay driver circuit open
- Fuel lift pump relay ground circuit open
- Fuel lift pump relay ground circuit shorted to external voltage
- ECM
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding.
Diagnostic Test
1. LIFT PUMP RUNS
Remove the cover to the PDC.
Turn the ignition on, engine off.
With the scan tool, in system test actuate the lift pump relay.
Q: Does the fuel lift pump relay click when the lift pump is actuated?
YES: Test complete.
Perform Intermittent Condition test.
NO: Go To 2
2. LIFT PUMP RELAY DOES NOT CLICK
Turn Ignition off.
Remove the lift pump relay from the PDC.
Turn the ignition on.
Connect one end of an incandescent test light to battery negative.
Connect the other end of the test light to the relay driver pin in the PDC.
With the scan tool, in system test actuate the lift pump relay.
Q: Does the test light illuminate brightly?
YES: Go To 3
NO: Go To 5
3. FUEL LIFT PUMP GROUND CIRCUIT OPEN
Connect one end of an incandescent test light to battery positive.
Connect the other end of the test light to the relay ground pin in the PDC.
Q: Is the resistance less than 1 Ohms?
YES: Go To 4
NO: Repair the open ground circuit. Perform the POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). Powertrain Verification Test - Ver 1
4. LIFT PUMP RELAY
Install a know good relay in place of the fuel lift pump relay.
With the scan tool, in system test actuate the lift pump relay.
Q: Does the fuel lift pump relay click when the lift pump is actuated?
NO: Go To 5
YES: Replace the lift pump relay. Perform the POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). Powertrain Verification Test - Ver 1
5. FUEL LIFT PUMP DRIVER CIRCUIT OPEN
Turn Ignition off.
Disconnect the ECM connectors.
NOTE: Check connectors - Clean/repair as necessary.
Using an ohmmeter, measure the resistance of the lift pump relay driver wire between the ECM connector and the PDC.
Q: Is the resistance less than 10 Ohms?
NO: Repair the Fuel lift pump driver circuit open. Perform the POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). Powertrain Verification Test - Ver 1
YES: Go To 6
6. FUEL LIFT PUMP RELAY DRIVER CIRCUIT SHORTED TO EXTERNAL VOLTAGE
Measure the voltage between battery negative and the relay driver circuit in the PDC.
Q: Is the voltage greater than 1 volt?
YES: Repair the Fuel lift pump Relay driver circuit shorted to voltage. Perform the POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). Powertrain Verification Test - Ver 1
NO: Go To 7
7. FUEL LIFT PUMP RELAY DRIVER CIRCUIT SHORTED TO OTHER CIRCUITS
Measure the resistance between the lift pump relay driver circuit in the ECM connector and all other circuits in the ECM connectors.
Q: Is the resistance less than 10 Ohms?
YES: Repair the Fuel lift pump Relay driver circuit shorted to another circuit. Perform POWERTRAIN VERIFICATION TEST VER - 1(DIESEL). Powertrain Verification Test - Ver 1
NO: Go To 8
8. ECM
Reconnect the ECM connectors.
Turn the ignition on, engine off.
Connect one end of an incandescent test light to battery negative.
Connect the other end of the test light to the relay driver pin in the PDC.
Using the scan tool, actuate the lift pump.
Q: Does the test light illuminate brightly?
YES: Repair complete. Perform the POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). Powertrain Verification Test - Ver 1
NO: Replace the ECM. Perform the POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). Powertrain Verification Test - Ver 1