Fuel and air

P0256 — Injection Pump Fuel Metering Control B Malfunction

Severity: medium Drive with care, to a shop

What P0256 means

The engine control module monitors the electronic fuel metering control in a diesel high-pressure injection pump. P0256 sets when the circuit B signal or current is outside the expected range, or the actuator does not deliver the commanded fuel quantity. The cause can be the metering solenoid, a position sensor, wiring or the pump itself.

Symptoms

  • Check Engine light on
  • Reduced power or limp mode
  • Rough idle and hesitation
  • Higher fuel consumption
  • Misfire-like shaking
  • Possible stalling or hard starting

Possible causes

  1. Faulty fuel metering solenoid or pump actuator
  2. Damaged wiring or corroded connector at the injection pump
  3. Failed fuel rack or metering position sensor
  4. Mechanical wear or failure of the injection pump
  5. ECM fault (unlikely)

How to diagnose

  1. Read all codes and freeze frame data, clear the code and see if it returns
  2. Inspect the pump harness and connector for breaks, chafing, corrosion and oil contamination
  3. Check power, ground and solenoid resistance against specifications
  4. Check the position sensor signal with a scan tool or oscilloscope
  5. Check fuel pressure and the condition of the fuel filter
  6. Compare fuel trim and cylinder balance, and check injector circuits
  7. Rule out air leaks in the intake and fuel lines
  8. If wiring and ECM check out, have the pump bench tested

Common fixes

  • Repair wiring and clean or replace connectors
  • Replace the metering solenoid or pump actuator
  • Replace the position sensor
  • Replace or rebuild the injection pump
  • Reflash or repair the ECM if a fault is confirmed

Questions and answers

What does P0256 mean?

It is a fault in fuel metering control circuit B of a diesel injection pump. The ECM sees that the metering device or its signal is not behaving as commanded.

Can I drive with P0256?

Only a short distance, carefully, to a shop. Power loss and stalling are possible, so do not put off diagnosis.

Do I need a new injection pump right away?

No. Check the wiring, connector, power supply and sensor first, since they are often the cause and the pump is expensive.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.