P0256 Diesel injection pump fuel metering control B malfunction (cam, rotor or injector)

Injection pump fuel metering control B malfunction

Severity not verified — if the car runs badly, have it inspected

The sources read define the code but do not rate how urgent it is. Hard starting, power loss and heavy smoke are listed as symptoms, so have a diesel shop check it rather than wait.

Source: how we rate severity

P0256 in short

P0256 is a diesel code meaning the computer found a fault in fuel metering control B on the injection pump. It sets when expected and actual fuel delivery do not match. Wiring, a clogged fuel filter and a faulty actuator or position sensor are the usual causes. Get it checked, as it can cause hard starting.

The Delaware DMV generic code list titles P0256 as Injection Pump Fuel Metering Control B Malfunction (cam, rotor, injector). TroubleCodes.net says it applies to diesel engines only.

TroubleCodes.net says the computer sets the code when the fuel delivered does not match what it expects. It lists wiring, a clogged fuel filter, the fuel control actuator or the fuel rack position sensor as the usual causes, and the pump itself as rare.

Most likely causes

These are general causes for this code across vehicles. None is specific to one make or model.

  1. Damaged, corroded or disconnected wiring or connectors

    Possible — needs testing
    Why it ranks here
    Wiring faults are the first cause TroubleCodes.net lists, and they are cheap to check before any part is replaced.
    What would change this
    Rises if a harness or plug is damaged. Falls if wiring and connectors test good.

  2. Clogged fuel filter

    Possible — needs testing
    Why it ranks here
    TroubleCodes.net lists a clogged fuel filter among the common causes, and it is a routine service item.
    What would change this
    Rises if the filter is overdue or restricted. Falls if it is clean.

  3. Faulty fuel control actuator or fuel metering sensor

    Possible — needs testing
    Why it ranks here
    The code compares what the computer asks the actuator to do with what the sensor reports, so a failed actuator or sensor sets it.
    What would change this
    Rises if electrical readings are out of specification. Falls if they are in specification.

  4. Failed injection pump or computer driver (rare)

    Possible — needs testing
    Why it ranks here
    TroubleCodes.net calls a pump or computer driver failure rare, so it ranks last.
    What would change this
    Rises only after wiring, filter and actuator are cleared.

What to test first

Start at step 1. Each result tells you what it means and where to go next.

  1. Read all stored codes and freeze-frame data with a scan tool and note any other fuel-system codes.

    Low riskTool: OBD-II scan tool

    • IfOther fuel-metering codes from the same pump are stored

      It meansTreat them as one problem and start with wiring and the actuator.

      Go to step 2

    • IfOnly this code is stored

      It meansCheck the wiring and fuel filter first.

      Go to step 2

  2. With the engine off, look over the fuel-metering actuator and sensor wiring and connectors for damage, corrosion or a loose plug, and check the fuel filter service history.

    Low risk

  3. Have the reference voltage, signal voltage, resistance and continuity of the fuel control actuator and position sensor tested against the manual.

    Best left to a shopTool: multimeter, scan tool

    Warning:Diesel injection systems run at very high fuel pressure and the pump is live while cranking. Do not open fuel lines or probe connectors with the engine running; a shop should do this.

Symptoms

  • Check engine light on
  • Hard starting or no start
  • Power loss, hesitation or rough running
  • Excess exhaust smoke
  • Worse fuel economy

How to fix

  1. With the engine off and cool, look over the visible wiring and plugs near the injection pump for damage or a loose connector.

  2. Check when the diesel fuel filter was last changed and have a shop service it if it is overdue.

Parts and cost context

  • Fuel pump:The injection or high-pressure pump is listed as a rare cause. Rule out wiring, filters and the actuator first. Labour varies; get a quote.

Labor varies by vehicle and shop; get a quote before you approve a repair.

Compare used part prices on PartPriceGuide

On your vehicle

We don't have reviewed vehicle-specific evidence for P0256 yet. The causes and tests above apply across vehicles.

No curated relationships for P0256 yet.

All Fuel pump and injectors codes

Sources and review

  1. P0256 and P0258 code pages — TroubleCodes.net
  2. On-Board Diagnostic Trouble Codes (generic code title list) — Delaware Division of Motor Vehicles
Last reviewed
Written by
Saurabh K.
Editorial review
Pending
Technician review
Technician review pending

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