P0256 Injection Pump Fuel Metering Control B Malfunction
OBD-II Trouble Code Technical Description
Injection Pump Fuel Metering Control B Malfunction (Cam/Rotor/Injector)
What does that mean?
This generic powertrain/engine diagnostic trouble code can typically apply to all diesel fueled OBD-II equipped engines (e.g. Ford, Chevy, GMC, Ram, etc.), but shows up more often in certain Mercedes Benz and VW vehicles.
Although generic, the exact repair steps may vary depending on year, make, model and powertrain configuration.
The Injection Pump Metering Control Circuit "B" is usually found mounted inside / on the side of the injection pump bolted to the engine. The Injection Pump Metering Control Circuit "B" is usually made up of a Fuel Rack Position (FRP) Sensor and a Fuel Quantity Actuator.
The FRP sensor converts the amount of diesel fuel being delivered by the Fuel Quantity Actuator to the injectors into an electrical signal for the Powertrain Control Module (PCM).
The PCM receives this voltage signal to determine how much fuel it will put into the engine based upon engine operating conditions. This code is set if this input does not match normal engine operating conditions stored in the PCM’s memory, even for a second, as this diagnostic trouble code demonstrates. It also looks at the voltage signal from the FRP sensor to determine if it is correct at initial Key On.
The code P0256 Injection Pump Fuel Metering Control B Malfunction (Cam/Rotor/Injector) could have been set because of mechanical (typically EVAP system mechanical issues) or electrical (FRP sensor circuit) issues. These cannot be overlooked in the troubleshooting stage, especially when dealing with an intermittent problem. Refer to a vehicle specific repair manual to determine which is the "B" part of the circuit for your particular application.
Troubleshooting steps may vary depending upon manufacturer, type of FRP sensor and wire colors.
What is the severity of this DTC?
Severity in this case will be not severe. Since it is electrical failure, the PCM can compensate adequately for it.
What are some of the symptoms of the code?
Symptoms of a P0256 trouble code may include:
Malfunction Indicator Lamp (MIL) illumination Decrease in fuel economyWhat are some of the common causes of the code?
Causes for this P0256 code may include:
Open in the signal circuit to the FRP sensor - possible Short to voltage in the signal circuit to the FRP sensor - possible Short to ground in the signal circuit to the FRP sensor - possible Open in power or ground at FRP sensor - possible Failed FRP Sensor - likely Failed PCM - unlikelyWhat are some P0256 troubleshooting steps?
A good starting point is always to check for technical service bulletins (TSB) for your vehicle. Your issue may be a known issue with a known fix put out by the manufacturer and can save you time and money during diagnosis.
Next, locate the FRP sensor on your vehicle. This sensor is usually found usually found mounted inside / on the side of the injection pump bolted to the engine. Once located, visually inspect the connector and wiring. Look for scraping, rubbing, bare wires, burn spots or melted plastic. Pull the connector apart and carefully inspect the terminals (the metal parts) inside the connector. See if they look burned or have a green tint indicating corrosion. Use electrical contact cleaner and a plastic bristle brush if cleaning of the terminals is needed. Let dry and apply electrical grease where the terminals contact.
If you have a scan tool, clear the diagnostic trouble codes from memory, and see if P0256 code returns. If it does not, then the connections were most likely your problem.
If the P0256 code does return, we will need to test the FRP sensor and its associated circuits. With t
Read: 41
