P025C

P025C-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:
Engine running. Battery voltage greater than 11.0 Volts.

- Set Conditions:
MIL code sets when the Fuel Pump Control Module (FPCM) detects a voltage on the FPCM Motor Feed circuit below the calibrated threshold. The PCM sets the code after the failure matures for 60 seconds.





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

Diagnostic Test

1. ACTIVE DTC

NOTE: If DTC P0627 is present, repair that DTC before proceeding with this test.

1. Ignition on, engine not running.
2. With the scan tool, select View DTCs.

Is the DTC Active at this time?

Yes

- Go To 2

No

- Perform the INTERMITTENT CONDITION Diagnostic Procedure. Intermittent Condition Test.

2. CHECK THE (N1) FPCM MOTOR FEED CIRCUIT FOR A SHORT TO GROUND
1. Turn the ignition off.
2. Disconnect the FPCM harness connector.
3. Remove the Fuel Pump Relay.
4. Measure the resistance between ground and the (N1) FPCM Motor Feed circuit at the FPCM harness connector.

Is the resistance < 10k ohms?

Yes

- Repair the short to ground in the (N1) FPCM Motor Feed circuit.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

No

- Go To 3

3. CHECK THE (N1) FPCM MOTOR FEED CIRCUIT FOR AN OPEN OR HIGH RESISTANCE
1. Turn the ignition off.
2. Measure the resistance of the (N1) FPCM Motor Feed circuit from the C1 PCM harness connector to the appropriate terminal of the Fuel Pump Relay socket in the PDC.

Is the resistance below 5.0 Ohms?

Yes

- Go To 4

No

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

4. FUEL PUMP CONTROL MODULE
1. Reconnect the Fuel Pump relay.
2. Leave the FPCM harness connector disconnected.
3. Turn the ignition on, engine not running.
4. With the scan tool, begin the Variable Speed Fuel Pump Relay Actuation Test.
5. Measure the voltage of the (N1) FPCM Motor Feed circuit.

Is the voltage the same as battery voltage?

Yes

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

No

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