P0629

P0629-FUEL PUMP CONTROL CIRCUIT HIGH







Theory of Operation

The Fuel Lift Pump Control circuit is a low side driver inside the Powertrain Control Module (PCM). Do to the nature in which this monitor runs, an open circuit or short to ground in the (K31) Fuel Lift Pump Control circuit will set this DTC. The Totally Integrated Power Module (TIPM) sends a 12 Volt signal to the PCM on the (K31) Fuel Lift Pump Control circuit at ignition on. The PCM grounds the control circuit from the TPIM to command the Fuel Lift Pump on. The TIPM then sends a 12 Volt feed to the Fuel Lift Pump. The Fuel Lift Pump grounds through a dedicated ground circuit. The MIL lamp and ETC lamp will illuminate immediately after this diagnostic runs and fails. During this time, the customer may experience engine stumble/stall or low power due to lack of fuel supply to the high pressure system. The PCM will turn off the MIL lamp once the diagnostic runs and passes in four consecutive drive cycles.

- When Monitored:
While the key is on.

- Set Condition:
The Fuel Lift Pump control is commanded on by the Powertrain Control Module (PCM), but feedback voltage is low.





Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. Pre-Diagnostic Troubleshooting Procedure.

1. ACTIVE DTC
1. Turn the ignition on.
2. With the scan tool, record all Freeze frame data.
3. With the scan tool, erase DTCs.
4. Turn the ignition off for 75 seconds.
5. Turn the ignition on.
6. With the scan tool, read DTCs.

Did the DTC return?

Yes

- Go To 2

No

- Perform the INTERMITTENT CONDITION - 6.7L diagnostic procedure. Intermittent Condition Test.

2. CHECK THE (K31) FUEL LIFT PUMP CONTROL CIRCUIT FOR A SHORT TO GROUND
1. Turn the ignition off.
2. Disconnect the PCM C2 harness connector.
3. Disconnect the TIPM C2 harness connector.
4. Measure the resistance between ground and the (K31) Fuel Lift Pump Control circuit at the PCM C2 harness connector.

Is the resistance below 10k Ohms?

Yes

- Repair the (K31) Fuel Lift Pump Control circuit for a short to ground.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

No

- Go To 3

3. CHECK THE (K31) FUEL LIFT PUMP CONTROL CIRCUIT FOR AN OPEN/HIGH RESISTANCE
1. Measure the resistance of the (K31) Fuel Lift Pump Control circuit between the PCM C2 harness connector and the TIPM C2 harness connector.

Is the resistance below 5.0 Ohms?

Yes

- Go To 4

No

- Repair the (K31) Fuel Lift Pump Control circuit for an open or high resistance.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

4. CHECK THE TOTALLY INTEGRATED POWER MODULE OUTPUT
1. Reconnect the PCM C2 harness connector.
2. Reconnect the TIPM C2 harness connector.

NOTE: Be careful to use only an appropriate back probing tool so as not to damage the terminal or connector in the next step.

3. Using a Voltmeter connected to ground, back probe the (K31) Fuel Lift Pump Control circuit at the TIPM C2 harness connector.
4. Turn the ignition on.

Does the Voltmeter read above 9.5 Volts with the ignition on?

Yes

- Go To 5

No

- Replace the Totally Integrated Power Module (TIPM).
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

5. POWERTRAIN CONTROL MODULE
1. With the scan tool, toggle the Fuel Lift Pump actuator on and off.

Does the Voltmeter read above 9.5 Volts with the lift pump toggled off and 0 Volts with the lift pump toggled on?

Yes

- Disconnecting and reconnecting the PCM AND TIPM harness connectors may have fixed the problem. Perform the INTERMITTENT CONDITION - 6.7L diagnostic procedure. Intermittent Condition Test.

No

- Replace the Powertrain Control Module (PCM).
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.