DTC P0251: FUEL INJECTION PUMP MECHANICAL FAILURE FUEL VALVE FEEDBACK CIRCUIT

Monitor & Set Conditions

The fuel injection pump mechanical failure fuel valve feedback circuit is monitored when the ignition is on. DTC may be stored when Engine Control Module (ECM) senses fuel command is within predetermined parameters, fuel pump battery voltage exists and fuel delivery valve solenoid is energized with greater than 9 volts.

Possible Causes

• Wiring/Connector Problem
• Verify Charging System Performance
• Battery Voltage Less Than 12 Volts
• Fuel Injection Pump Ground Circuit Open
• Fuel Injection Pump Relay Output Circuit Open
• Fuel Injection Pump Relay Ground Circuit Open
• Fused B+ Circuit Open To Fuel Injection Pump Relay
• Fuel Injection Pump Relay Output Circuit Open
• Fuel Injection Pump Relay
• Fuel Injection Pump

Testing

1. Turn ignition on with engine off. Using DRBIII(R) scan tool, check for any other fuel injection pump related DTCs. If no other fuel injection pump related DTC exists, go to next step. If any other fuel injection pump related DTC exist, diagnose those DTC first.

2. Ensure ignition is on with engine off. Using scan tool, check for DTCs. If Good Trip Counter for DTC P0251 is not equal to zero, go to next step. If Good Trip Counter for DTC P0251 is equal to zero, go to step 5.

3. Ensure ignition is on with engine off. Using scan tool, read FREEZE FRAME data. Operate vehicle within FREEZE FRAME data parameters while wiggling wiring harness and connectors between Fuel Pump Control Module (FPCM) and ECM, and between fuel pump relay and FPCM. FPCM is located on the end of fuel injection pump. FPCM is incorporated into fuel injection pump and may also be referred to as the fuel injection pump when referencing to the wiring diagram. ECM is located on driver's side of the engine, just in front of fuel transfer pump and contains a 50-pin connector. Fuel pump relay is located in PDC at driver's side front corner of engine compartment. Fuel pump relay may also be referred to as fuel injection pump relay. If the STARTS SINCE SET counter changes to zero, go to next step. If STARTS SINCE SET counter does not change to zero, the test is complete.

4. Turn ignition off. Inspect wiring and connectors between FPCM and ECM, and between fuel pump relay and FPCM. If no problems exist, go to next step. If any problems exist, repair wiring or connectors as necessary.

5. Check charging system operation. Perform TEST CH-1A: CHARGING SYSTEM NO CODE TEST under SYSTEM TESTS in GENERATORS & REGULATORS - TRUCKS & RWD VANS article. If the charging system is operating properly, go to next step. If the charging system is not operating properly, repair as necessary.

6. Ensure ignition is off. Using DVOM, measure voltage between battery terminals. If the voltage is 12 volts or greater, go to next step. If the voltage is less than 12 volts, recharge or replace the battery as necessary.

7. Ensure ignition is off. Disconnect FPCM harness connector. FPCM connector is located on the end of fuel injection pump. Check for poor connection/terminal contact at FPCM harness connector. Repair as necessary. Turn ignition on with engine off. Connect a test light between ground and terminal No. 7 (Red/Light Green wire) on FPCM connector. If test light illuminates brightly, go to next step. If test light does not illuminate brightly, go to step 9.

8. Turn ignition off. Ensure FPCM connector is still disconnected. Using DVOM, measure resistance between ground and terminal No. 6 (Black/Tan wire) on FPCM connector. If resistance is less than 5 ohms, the test is complete. If resistance is 5 ohms or greater, repair open in Black/Tan wire between FPCM and ECM.

9. Turn ignition off. Remove fuel pump relay from Power Distribution Center (PDC). PDC is located at driver's side front corner of engine compartment. Fuel injection pump relay may also be referred to as fuel pump relay. Check for poor connection/terminal contact at the fuel pump relay. Repair as necessary. Turn ignition on with engine off. Connect a test light between ground and cavity No. 86 (Brown/White wire) in PDC for fuel pump relay. If test light illuminates brightly, go to next step. If test light does not illuminate brightly, repair open in Brown/White wire between terminal No. 36 on ECM harness connector and cavity No. 86 in PDC for fuel pump relay.

10. Turn ignition off. Using DVOM, measure resistance between ground and cavity No. 85 (Black wire) in PDC for fuel pump relay. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or greater, repair open in Black wire between cavity No. 85 (Black wire) in PDC for fuel pump relay and ground connection. The ground connection is located on cylinder block, just below fuel transfer pump.

11. Connect a test light between ground and cavity No. 30 (Red/White wire) in PDC for fuel pump relay. This is the fused B+ circuit from the battery to fuel pump relay. If test light illuminates brightly, go to next step. If test light does not illuminate brightly, repair open in Red/White wire between cavity No. 30 in PDC for fuel pump relay and fuse No. 3 (20-amp). Fuse No. 3 receives a constant battery voltage and is located in PDC.

12. Using DVOM, measure the resistance of Red/Light Green wire between cavity No. 87 in PDC for fuel pump relay and terminal No. 7 on FPCM connector. If resistance is less than 5 ohms, the test is complete. If resistance is 5 ohms or greater, repair open in Red/Light Green wire between FPCM connector and PDC.