P0628

P0628-FUEL PUMP CONTROL CIRCUIT LOW

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:
With the ignition on. Battery voltage greater than 10.4 Volts and the ASD sense switch is on.

- Set Condition:
MIL code sets if the Fuel Pump Control Module (FPCM) detects a signal on the FPCM Pump Feed circuit that is lower than the calibrated threshold.





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

Diagnostic Test

1. ACTIVE DTC

NOTE: If DTC P025A, P0627, or P1205 are present, repair that DTC before proceeding with this test.

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 (N13) FPCM PUMP FEED CIRCUIT FOR A SHORT TO GROUND
1. Turn the ignition off.
2. Disconnect the FPCM harness connector.
3. Measure the resistance between ground and the (N13) FPCM Pump Feed circuit at the FPCM harness connector.

Is the resistance less than 10k ohms?

Yes

- Repair the (N13) FPCM Pump Feed circuit for a short to ground.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

No

- Go To 3

3. CHECK THE (N13) FPCM PUMP FEED CIRCUIT FOR AN OPEN OR HIGH RESISTANCE
1. Leave the ignition off.
2. Leave the FPCM harness connector disconnected.
3. Disconnect the PCM C1 harness connector.
4. Measure the resistance of the (N13) FPCM Pump Feed circuit from the FPCM harness connector to the PCM C1 harness connector.

Is the resistance below 5.0 Ohms?

Yes

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

No

- Repair the (N13) FPCM Pump Feed circuit for an open or high resistance.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test