Faulty or sticking fuel metering valve or quantity actuator in the injection pump; Wiring or connector fault in the metering control circuit (high resistance, corrosion, chafed or broken wires); Low fuel supply pressure from a blocked fuel filter, air ingress or weak lift pump; Worn internal pump components such as cam ring, rotor or vanes, causing poor metering accuracy; Contaminated or poor quality fuel, or water in the fuel, affecting pump operation; Incorrect pump timing or a faulty pump position or timing feedback sensor; Fault in the engine control unit driver circuit.

P0257

Injection Pump Fuel Metering Control B Range/Performance (Cam/Rotor/Injector).

Generic
Powertrain
Generic code
Medium severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
2: AreaFuel and air metering (injector circuit)
57: FaultThe specific fault in that area

What it means

P0257 is the generic code for a range or performance fault in the 'B' fuel metering control of the injection pump, relating to the cam, rotor or injector side of the pump. It is mainly seen on diesels with a rotary or distributor-type injection pump. The engine control unit has seen the commanded fuel metering and the actual response (such as metering valve, quantity actuator or feedback position) disagree or fall outside the expected range.

Symptoms

Engine warning light on
Hard starting or long cranking, especially when hot
Rough idle or hunting idle
Loss of power or limp mode
Black or white smoke under load
Engine stalling or surging

Possible causes

Faulty or sticking fuel metering valve or quantity actuator in the injection pumplikely
Wiring or connector fault in the metering control circuit (high resistance, corrosion, chafed or broken wires)likely
Low fuel supply pressure from a blocked fuel filter, air ingress or weak lift pumplikely
Worn internal pump components such as cam ring, rotor or vanes, causing poor metering accuracypossible
Contaminated or poor quality fuel, or water in the fuel, affecting pump operationpossible
Incorrect pump timing or a faulty pump position or timing feedback sensorpossible
Fault in the engine control unit driver circuitrare

How to diagnose

Read all stored and pending codes and the freeze frame data, noting engine speed, load and temperature when the fault set, and check for related fuel or sensor codes.
Check for technical service bulletins and known pump issues for the specific model and engine, as pump design and the meaning of 'B' circuit vary.
Inspect the fuel filter, water separator and fuel lines for blockage, water, leaks and air ingress, and check the fuel for contamination.
Visually inspect the pump wiring and connectors for damage, corrosion, heat damage and poor pin tension.
Test the metering valve or actuator circuit for supply, earth, signal and resistance against the manufacturer's specification.
Measure fuel supply and return pressure or flow to confirm the lift pump and fuel system are delivering correctly.
Check live data for commanded versus actual metering or pump position while running and compare against specification.
Check pump timing and the related position sensor signals, following the procedure for that engine.

How to fix

Repair or replace damaged wiring, terminals or connectors in the metering control circuit.
Replace the fuel filter, drain water and clear air from the system, then repair any leaks or faulty lift pump.
Replace or recondition the metering valve or quantity actuator if it is out of specification.
Repair or replace the injection pump if internal wear or poor metering is confirmed.
Drain and flush contaminated fuel and refill with good quality fuel.
Reset the pump timing or replace the faulty position sensor, then clear the codes and road test.

Can I keep driving?

Medium severity

The car can usually be driven for a short time if it runs reasonably, but get it checked soon as poor metering can cause stalling, loss of power and further pump or engine damage. Avoid heavy loads and long journeys, and stop if it stalls repeatedly or goes into limp mode.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.