Injection Pump Fuel Metering Control A Malfunction (Cam/Rotor/Injector)
P0251 indicates a malfunction in the fuel injection pump's metering control system, typically affecting diesel engines. The engine computer has detected an issue with the fuel rail pressure (FRP) sensor circuit or the injection pump's ability to properly regulate fuel delivery.
What You Might Notice
- Check Engine Light illuminated
- Decreased fuel economy
- Rough idle or hesitation during acceleration
- Reduced engine power or performance
- Possible white or black smoke from exhaust
Most Common Causes
- 1
Fuel Rail Pressure (FRP) Sensor Circuit Open
A break or loose connection in the wiring or connector between the FRP sensor and the engine control module prevents the computer from reading fuel pressure data accurately.
- 2
FRP Sensor Short to Voltage
The sensor signal circuit is shorted to the positive voltage supply, causing the controller to receive incorrect pressure readings and unable to control fuel metering properly.
- 3
FRP Sensor Short to Ground
The signal circuit is shorted to ground, preventing proper voltage communication between the sensor and engine computer.
- 4
Injection Pump Mechanical Failure
Internal wear or failure of the fuel injection pump's cam, rotor, or injector components reduces the pump's ability to meter fuel correctly.
How to Diagnose It
- 1
Check Fuel Rail Pressure (FRP) Sensor Circuit Open — A break or loose connection in the wiring or connector between the FRP sensor and the engine control module prevents the computer from reading fuel pressure data accurately.
- 2
Check FRP Sensor Short to Voltage — The sensor signal circuit is shorted to the positive voltage supply, causing the controller to receive incorrect pressure readings and unable to control fuel metering properly.
- 3
Check FRP Sensor Short to Ground — The signal circuit is shorted to ground, preventing proper voltage communication between the sensor and engine computer.
- 4
Check Injection Pump Mechanical Failure — Internal wear or failure of the fuel injection pump's cam, rotor, or injector components reduces the pump's ability to meter fuel correctly.
How to Fix It
- 1
Inspect and Repair FRP Sensor Circuit
Check the fuel rail pressure sensor connector and wiring harness for corrosion, loose connections, or damage. Repair or replace damaged wiring and connectors as needed.
- 2
Replace Fuel Rail Pressure Sensor
Test the FRP sensor with a multimeter to confirm it is faulty, then remove and replace with a new sensor rated for your specific vehicle and diesel engine type.
- 3
Inspect Fuel Injection Pump Assembly
Remove the injection pump and visually inspect the internal components (cam, rotor, injectors) for wear, scoring, or damage. Have a diesel specialist evaluate the pump's condition.
- 4
Replace Fuel Injection Pump
If the pump is worn or damaged internally and cannot be repaired, the entire injection pump assembly must be replaced and the system primed and bled to remove air.
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