P0259
Injection Pump Fuel Metering Control B High (Cam/Rotor/Injector).
- Generic
- Powertrain
- Generic code
- High severity
How this code is built
- P
- SystemPowertrain
- 0
- Defined bySAE, the same on every car
- 2
- AreaFuel and air metering (injector circuit)
- 59
- FaultThe specific fault in that area
What it means
P0259 is a generic powertrain code meaning the engine control unit has detected a high signal or circuit condition in the fuel metering control 'B' circuit of a diesel injection pump (cam, rotor or injector type). The control unit commands the metering device and monitors the circuit and the resulting response. It set the code because the circuit voltage or current was higher than expected, or the commanded and actual metering did not agree. The exact layout of circuit 'B' depends on the engine and pump design.
Symptoms
- Engine management warning light on
- Hard starting or no start
- Rough idle or uneven running
- Loss of power or limp mode
- Engine stalling or surging
- Black or white smoke from the exhaust
Possible causes
- Wiring fault in the metering control circuit B, such as a short to voltage or chafed insulationlikely
- Corroded, loose or damaged connector at the pump or control unitlikely
- Faulty fuel metering valve or solenoid in the injection pumplikely
- Faulty injection pump internal control or driver electronics (on pumps with an integral control module)possible
- Low or unstable supply voltage from a weak battery or charging faultpossible
- Fault in the engine control unit output driverrare
- Outdated control unit software where the manufacturer has issued a known fix for the modelrare
How to diagnose
- Read all stored and pending codes and note the freeze frame data to see engine speed, load and temperature when the fault set.
- Check for other related codes, such as fuel rail, pump timing or supply voltage faults, and deal with those first if present.
- Visually inspect the wiring and connectors between the injection pump and the control unit for chafing, heat damage, corrosion, water ingress and bent or pushed-back pins.
- Test battery condition and charging voltage, as low or erratic voltage can cause circuit faults.
- With the ignition off and connectors disconnected, check the circuit B wiring for continuity, short to voltage and short to earth using the manufacturer's wiring diagram.
- Measure the resistance of the metering valve or solenoid and compare it with the specification for that engine.
- Using a scan tool with live data, compare commanded and actual metering values and watch for the fault returning when the harness is gently moved.
- Check for a software update or technical bulletin for the specific model and engine before replacing expensive parts.
How to fix
- Repair or replace damaged wiring and fix any short to voltage in circuit B.
- Clean, repair or replace corroded or damaged connectors and terminals.
- Replace the fuel metering valve or solenoid if it is out of specification and the pump design allows it.
- Replace or professionally overhaul the injection pump if its internal electronics or metering unit has failed.
- Correct battery or charging system faults to restore stable supply voltage.
- Update the control unit software only if a manufacturer-approved update exists for this fault on that model.
Can I keep driving?
Avoid driving if the engine is running poorly, stalling or in limp mode, as uncontrolled fuel metering can cause loss of power and potential engine damage. If it drives normally, keep journeys to a minimum and have it diagnosed promptly.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.