Error Code P0256: What It Means & What To Do?

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Is your car engine misfiring and having delayed start up? Is there black smoke emitting from the car exhaust? Is there a sudden drop in the fuel economy? All these are the indications to the OBD Code P0256 being stored and flashed in the Powertrain Control Module (PCM).

OBD-II Code Decreased engine performance is defined as an Injection Pump Fuel Metering Control "B" (Cam/Rotor/Injector)

OBD II fault code P0256 is a generic code that is defined as “Injection Pump Fuel Metering Control “B” Malfunction (Cam/Rotor/Injector)”, and is set on diesel applications when the PCM (Powertrain Control Module) detects that the volume of fuel being delivered to the injectors does not agree with the volume that is expected to be delivered given the current operating conditions.

Diesel applications use sophisticated control mechanisms and controllers to control both the volume of fuel injected, and to manage the timing of the injection event. Using input data from the throttle pedal position sensor, the PCM calculates the volume of fuel required to suit current operating conditions; a Fuel Control Actuator (aka “fuel quantity adjuster”) that is located either in or near the main injection pump then delivers the required volume of fuel to the injectors.

However, the PCM needs to know how much fuel is actually being delivered, so it uses a dedicated sensor, known as the Fuel Rack Position sensor, to monitor the position of the Fuel Control Actuator, and to signal this information back to the PCM.

What causes the problem of Injection Pump Fuel Metering Control B Malfunction (Cam/Rotor/Injector)?

• Clogged/damaged fuel filter
• Fuel pump fault/failure
• Fuel injector fault/failure
• PCM (Powertrain Control Module) faulty
• Faulty fuel pressure sensor
• Electric fuel pressure regulator faulty
• Fuel filter or other parts of the fuel system clogged/restricted
• Damaged wiring such as a short to ground

1. Diagnostic Tools - Use factory grade OBD scan tools to diagnose an OBD code error problem. Buy quality diagnostic tools from us now!
2. Powertrain Control Module - Although this error is rare, but check for faulty PCM and if it requires reprogramming or not. Find quality components from us.
3. Fuel Filter - If the fuel filters are damaged or clogged, they need immediate replacement for proper fuel delivery. Replace it now!
4. Fuel Pressure Sensor - It is important for the sensor to work properly for it to give right information to the PCM. Replace faulty pressure sensor now!
5. Fuel Control Actuator - Check for any faults within the control actuator and replace it immediately.
6. Fuel Pump - Check for leakages and damaged in the fuel pump and replace it if found damaged as it will affect the fuel delivery system
   

P0256 is considered severe since it may lead to a variety of drivability issues and cause internal engine and fuel delivery system damages.

Common Symptoms

• Delayed cold start and decreased engine performance
• Black smoke emission from the exhaust system
• Affected fuel efficiency
• Engine Misfires codes stored
• Rough idle and reduced throttle response. 

Following components can be replaced to solve OBD code P0256.

• Replacement of Fuel pressure regulator
• Replacement of Fuel pump
• Replacement of Fuel filter
• Replacement of faulty fuel injectors or other fuel system related sensors
• Repairing or replacing electrical wiring or connectors
• Replacement of Faulty fuel pump relay
• Removal of defective fuel pump relay
• Installation of new fuel pump relay
• Testing the fuel pressure and codes cleared with a scanner or gauge

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A mechanic may start with a good visual inspection of the fuel system and the associated components like fuel tank, fuel pump, fuel filter, lines and hoses, electrical wiring & connectors, sensors and injectors.

Examine other problematic parts of your vehicle's fuel injector and pump and replace them if needed. If the voltage reading is too high or low, suspect for a faulty injector and replace it immediately.

The injector circuit should also be tested for faulty connection or problems and should be resolved immediately.

During an inspection, make note of any damages to the system and repair them before proceeding with the diagnosis.

After performing the visual inspection, perform a fuel pressure test to test the functionality of all fuel system sensors.

If all the parts are checked for perfect operation, then suspect for faults in the Powertrain Control Module (PCM). Although, this error is rare but faulty components should be repaired or replaced and the system should be reprogrammed for eliminating any error.

Common Mistakes When Diagnosing The P0256 Code

Sometimes, mechanics will see a trouble code and take that for what is actually wrong with the car. Just because a particular part is mentioned in a trouble code, it does not mean that the part is faulty.

Always check for the following components as well while diagnosing this OBD code error P0256.

• Damaged or contaminated spark plug
• Engine sensor failure
• Exhaust leak
• Fuel injector failure
• Fuel pump failure
• Internal engine failure
• Powertrain Control Module (PCM) software needs to be updated
• The fuel does not meet the manufacturer's requirements