Damaged, chafed or corroded wiring or loose connector at the injection pump or metering control actuator; Faulty fuel metering valve or actuator inside the injection pump with an intermittent internal fault; Low or unstable supply voltage from a weak battery, poor earth or high resistance in a power feed; Air in the fuel, a restricted filter or poor lift pump supply affecting the pump's metering response; Worn injection pump internals (cam, rotor or related parts) causing inconsistent metering; Intermittent fault inside the engine control unit or pump driver circuit.

P0255

Injection Pump Fuel Metering Control A Intermittent (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)
55: FaultThe specific fault in that area

What it means

P0255 is the SAE J2012 generic code for an intermittent fault in the injection pump fuel metering control circuit A on a diesel engine. The engine control unit has seen the metering control signal or its feedback drop out or go out of range from time to time, rather than constantly. The exact design (cam, rotor or injector based pump) and the way the fault is detected depend on the engine and pump type.

Symptoms

Engine misfires, hesitates or surges at random
Intermittent loss of power or limp mode
Occasional hard starting or stalling
Engine warning light on, sometimes coming and going
Rough or uneven idle
Black or white smoke at times

Possible causes

Damaged, chafed or corroded wiring or loose connector at the injection pump or metering control actuatorlikely
Faulty fuel metering valve or actuator inside the injection pump with an intermittent internal faultlikely
Low or unstable supply voltage from a weak battery, poor earth or high resistance in a power feedpossible
Air in the fuel, a restricted filter or poor lift pump supply affecting the pump's metering responsepossible
Worn injection pump internals (cam, rotor or related parts) causing inconsistent meteringpossible
Intermittent fault inside the engine control unit or pump driver circuitrare

How to diagnose

Read all stored and pending codes and the freeze frame data to see engine speed, load and temperature when the fault set, and note any related fuel pressure or rail codes
Check the battery condition and charging voltage, and inspect the main power and earth connections
Visually inspect the injection pump wiring harness and connector for chafing, heat damage, oil contamination, bent pins and corrosion
With the engine running, gently wiggle the harness and connector while watching live data for dropouts or fault flicker
Check the fuel supply: filter condition, lines for air leaks, and lift pump delivery, following the manufacturer's procedure for the engine
Compare commanded and actual metering or fuel quantity values in live data, and test the actuator circuit resistance and signal against the manufacturer's specifications
Check for technical service bulletins or software updates for the model, as procedures vary by engine
Test the control unit driver circuit and pump only after the wiring and supply checks have passed

How to fix

Repair or replace damaged wiring and clean or replace faulty connectors and terminals
Restore good power and earth connections and replace a weak battery if needed
Replace the fuel metering valve or actuator, or the injection pump, if testing confirms an internal fault
Replace a blocked fuel filter, repair air leaks and fix lift pump supply problems
Update or correct the control unit calibration only if the manufacturer lists an outdated calibration as a known cause for this fault

Can I keep driving?

Medium severity

The car can usually be driven for a short time, but the fault may bring on limp mode or stalling without warning. Get it checked soon, and avoid long journeys or driving in traffic where a sudden loss of power would be unsafe.

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