What it means
Injection Pump Fuel Metering Control B (Cam/Rotor/Injector): the control module has detected this fault condition. This affects fueling of the associated cylinders.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
- The engine or gearbox may go into limp mode
How it works
Injection-pump fuel metering control B regulates fuel delivery through the pump's B control path; its exact hardware depends on the engine. The control module monitors control B and related fueling feedback. P0256 sets when it detects a fault in that control, which can disrupt fuel delivery to the cylinders supplied by the pump.
Common causes
Most likely first.
- Fuel metering actuator or valve B failure
- Damaged wiring or connector
- Fuel supply or pressure problem
- Injection pump fault
Symptoms
- Check-engine light on
- Hard starting or no start
- Rough running
- Reduced engine power
How to diagnose it
- Record freeze-frame data and check stored codes and live fuel-pressure or metering data to identify when the fault occurs.
- Inspect the control B connector and harness for loose pins, corrosion, damage, or contact with hot or moving parts.
- Check the fuel supply for restrictions, air leaks, or contamination that could affect pump metering.
- Compare commanded and reported metering-control B operation with scan data, if available.
- Test control B's circuit and the injection pump against the manufacturer's specification before replacing components.
Common fixes
- Clean and secure the control B connector or repair its damaged wiring.
- Replace a restricted fuel filter or repair a fuel-supply leak, as applicable.
- Replace a failed fuel-metering actuator or valve B after confirming the circuit is sound.
- Repair the injection pump if testing confirms an internal fault.
Can I keep driving?
Avoid driving if the engine is hard to start, stalls, runs roughly, or has sharply reduced power; it may lose power in traffic or fail to restart. If it runs smoothly, limit the trip and load until the fueling fault is diagnosed.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.