U0109

U0109-LOST COMMUNICATION WITH FUEL PUMP CONTROL MODULE

For a complete wiring diagram, refer to the Wiring Information.





Theory of Operation

When the Powertrain Control Module (PCM) receives a 'Start' or 'Run' signal from the ignition; It energizes the Fuel Pump relay which sends a continuous 12 volt supply to the Fuel Pump Control Module (FPCM). The PCM also sends a control signal directly to the FPCM which regulates the Pulse Width Modulated (PWM) voltage that will be sent to the Fuel Pump Module. The PWM will vary from 10-100% depending on the input of the Fuel Rail Pressure sensor and other engine demands. The Powertrain Control Module (PCM) receives a Pulse Width Modulated (PWM) signal from the Fuel Pump Control Module (FPCM) representing the state of all inputs and outputs of the FPCM. This is a Constant Pressure Fuel system which means any Delta Pressure test performed on the Fuel Pump would show a continuous pressure (regardless of the changes in PWM). If a pressure sensor fails or other failures are present; The duty cycle goes to Limp mode (100%) to maintain fuel pressure.

- When Monitored:
Engine running. Battery voltage greater than 11.0 volts.

- Set Conditions:
The Powertrain Control Module (PCM) does not receive a Pulse Width Modulated (PWM) signal from the Fuel Pump Control Module (FPCM). When this DTC is active, The FPCM will continue to run the Fuel Pump assembly at 100% duty cycle.





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

Diagnostic Test

1. ACTIVE DTC
1. Turn the ignition on, engine not running.
2. With the scan tool, read DTCs.

Is the DTC active?

Yes

- Go To 2

No

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

2. CHECK THE (N12) FPCM FEEDBACK RETURN CIRCUIT FOR A SHORT TO VOLTAGE
1. Leave the ignition on, engine not running.
2. Disconnect the FPCM harness connector.
3. Measure the voltage of the (N11) Control circuit at the FPCM harness connector.

Does the voltage measure above 5.2 volts?

Yes

- Repair the (N12) FPCM Feedback Return circuit for a short to voltage.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

No

- Go To 3

3. CHECK THE (N12) FPCM FEEDBACK RETURN CIRCUIT FOR A SHORT TO GROUND
1. Turn the ignition off.
2. Disconnect the PCM C1 harness connector.
3. Measure the resistance between ground and the (N12) FPCM Feedback Return circuit at the FPCM harness connector.

Is the resistance above 10k ohms?

Yes

- Go To 4

No

- Repair the (N12) FPCM Feedback Return circuit for a short to ground.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

4. CHECK THE (N12) FPCM FEEDBACK RETURN CIRCUIT FOR AN OPEN/HIGH RESISTANCE
1. Leave the ignition off.
2. Measure the resistance of the (N12) FPCM Feedback Return circuit between the FPCM harness connector and the PCM C1 harness connector.

Is the resistance below 5.0 ohms?

Yes

- Replace the Fuel Pump Control Module (FPCM).
- Go To 5

No

- Repair the (N12) FPCM Feedback Return circuit for an open or high resistance.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

5. POWERTRAIN CONTROL MODULE
1. Let the engine run until it reaches normal operating temperature.
2. Using the scan tool, record any DTCs.

Did the DTC return?

Yes

- Replace the Powertrain Control Module.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

No

- Repair is complete.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.