P0629

P0629-HIGH VOLTAGE DETECTED AT THE FUEL LIFT PUMP

P0629 - High 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
- Damaged wiring harness
- Lift pump relay driver circuit shorted to ground
- Lift pump relay
- 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. 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 4

YES: Replace the lift pump relay. Perform the POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). Powertrain Verification Test - Ver 1

4. FUEL LIFT PUMP RELAY DRIVER CIRCUIT SHORTED TO GROUND
Measure the resistance between battery negative and the relay driver circuit in the PDC.

Q: Is the resistance less than 10 ohms?

YES: Repair the Fuel lift pump Relay driver circuit shorted to ground. Perform the POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). Powertrain Verification Test - Ver 1
NO: Go To 5

5. 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 the POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). Powertrain Verification Test - Ver 1
NO: Go To 6

6. 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