Fault code P0251 – a step-by-step guide to diagnosing and fixing it

Error code P0251 is displayed and the check engine light is on - what does this mean?

The OBD system detects a fault in the injection pump control circuit (Injection Pump Fuel Metering Control "A" Malfunction). This DTC P0251 mainly occurs in diesel vehicles and affects the fuel metering of the injection pump. For various manufacturers, the code can also be interpreted as a fault in the fuel quantity control or injection control.

What causes can this error code have?

• Defective injection pump or its control valve
• Damaged fuel quantity regulator
• Faulty wiring to the injection pump control unit
• Defective fuel pressure sensor
• Clogged or dirty fuel filter
• Loose or corroded plug connections
• Defective engine control unit (ECU)
• Mechanical problems with the injection pump
• Incorrect fuel quality or contaminated fuel

What symptoms occur in parallel with fault code P0251?

• Starting problems: The vehicle is difficult to start or does not start at all
• Power loss: Significantly reduced engine power, especially under load
• Smooth engine running: Engine runs unevenly or jerks when idling
• Increased fuel consumption: Noticeably higher diesel consumption than usual
• Black smoke: Dark exhaust fumes from the exhaust, especially when accelerating
• Check engine light: Permanently lit or flashing warning light
• Emergency running program: Engine switches to emergency running mode with limited power

How can the problem with fault code P0251 be rectified?

• Repairing fault code P0251 requires a systematic approach to identify the exact source of the fault.
• Change the fuel filter and flush the fuel system: Remove the old fuel filter, install a new filter and flush the entire fuel system with clean diesel to remove impurities
• Professionally overhaul or replace the injection pump: Remove the injection pump and have it overhauled by a specialist workshop or replace it with an overhauled pump, including calibration on the test bench
• Check and replace fuel pressure sensor and wiring: Test fuel pressure sensor with multimeter, check wiring harness for continuity and insulation faults and replace defective components
• Diagnose engine control unit and replace if necessary: Test ECU with professional diagnostic technology, carry out software update or, if irreparably defective, replace the control unit with a programmed spare part
• Clean or replace the fuel flow regulator: Remove flow regulator, clean with special cleaner and check for correct function or replace with new part if defective