P0257 indicates the powertrain control module (PCM) has detected the fuel metering control signal on the injection pump's 'B' circuit is outside its expected range or behaving erratically. The code applies primarily to diesel engines with electronic distributor/inline injection pumps that use a fuel metering actuator (solenoid or valve) to regulate injection quantity and timing.
The metering solenoid itself is the most common failure. Internal coil winding breakdown, sticking pintle, or worn internal components cause the duty cycle / current feedback to drift outside the calibrated range.
Chafed insulation, broken wires, corroded pins, water intrusion at the pump-side connector, or poor chassis grounds frequently produce this code before the pump itself is at fault.
A weak lift/transfer pump, restricted fuel filter, water-in-fuel, or air ingress prevents the injection pump from developing required rail pressure, causing the metering actuator to overwork and flag a range/performance fault.
Mechanical wear inside the pump changes fuel delivery characteristics so the actuator can no longer keep the actual quantity within the PCM's expected window, especially at idle or high load.
If the PCM is acting on a false demand signal, it commands a metering position the pump cannot sustain, and a P0257 can be set even with a healthy pump.
A failed output driver, internal solenoid control short, or an outdated calibration can set this code, but this is the least common cause and is frequently misdiagnosed. Always rule out the pump, wiring, and fuel system first.
No. The code is set when the actual metering signal falls outside the expected range, and that is more often caused by the metering solenoid, its wiring/connector, or a fuel supply problem than by the pump body itself. The pump should only be suspected after the actuator, harness, and fuel delivery are verified.
Almost never. The PCM is one of the least common causes of P0257, yet it is frequently replaced unnecessarily when the real fault is a wiring problem, a failed metering solenoid, or a fuel delivery issue. Replace or reprogram the PCM only after the actuator, wiring, fuel system, and ground paths have all been ruled out, and only with confirmed evidence of a driver or internal ECU fault.
It is not advisable. Many vehicles will enter a power-reduction mode, and continued operation with incorrect fuel metering can cause elevated exhaust temperatures, soot loading, and in some cases internal pump or engine damage. Diagnose and repair before extended driving.
It is overwhelmingly a diesel code tied to electronic rotary or inline injection pumps. On port-fuel-injection gasoline engines the equivalent fuel metering faults use different DTCs, so seeing P0257 strongly suggests a diesel powertrain.