Technical Description of OBD-II Trouble Code
The performance of the Injection Pump Fuel Metering Control B (Cam/Rotor/Injector) is outside the expected range, causing a trouble code in the powertrain/engine diagnostic system. This code is commonly found in diesel fueled OBD-II equipped engines, particularly in certain Mercedes Benz and VW vehicles. However, the specific repair steps may vary depending on the year, make, model, and powertrain configuration of the vehicle.
The Injection Pump Metering Control Circuit “B” is typically located inside or on the side of the injection pump, which is bolted to the engine. It consists 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 into an electrical signal for the Powertrain Control Module (PCM). The PCM uses this signal to determine the appropriate amount of fuel to inject into the engine based on its operating conditions. The trouble code is triggered if the input from the FRP sensor does not match the expected engine operating conditions stored in the PCM’s memory, even for a brief moment.
The code P0257 Injection Pump Fuel Metering Control B Range/Performance (Cam/Rotor/Injector) can be caused by mechanical issues, such as problems with the EVAP system, or electrical issues, such as a malfunctioning FRP sensor circuit. It is important to address these potential causes during the troubleshooting process, especially when dealing with intermittent problems. Consult a vehicle-specific repair manual to identify the specific “B” part of the circuit for your particular application. The troubleshooting steps may also vary depending on the manufacturer, type of FRP sensor, and wire colors.
Severity of this DTC
The severity of this trouble code depends on the nature of the failure. If it is a mechanical failure, it can be severe. However, if it is an electrical failure, it is not as severe because the PCM can compensate adequately for it.
Symptoms of the code
Some symptoms that may be associated with a P0257 trouble code include:
Common causes of the code
Some common causes for the P0257 code include:
Troubleshooting steps for P0257
It is always a good idea to check for technical service bulletins (TSB) for your vehicle as a starting point. There may be a known issue with a known fix provided by the manufacturer, which can save time and money during diagnosis.
Next, locate the FRP sensor on your vehicle, which is usually mounted inside or on the side of the injection pump bolted to the engine. Inspect the connector and wiring visually, looking for any signs of damage such as scraping, rubbing, bare wires, burn spots, or melted plastic. Disconnect the connector and inspect the terminals inside for any signs of burning or corrosion. Clean the terminals if necessary using electrical contact cleaner and a plastic bristle brush, then apply electrical grease to ensure proper contact.
If you have a scan tool, clear the diagnostic trouble codes from memory and see if the P0257 code returns. If it does not, the issue was likely related to the connections.
If the P0257 code does return, further testing of the FRP sensor and its associated circuits is necessary. With the Key Off, disconnect the electrical connector at the FRP sensor and use a Digital Voltmeter to check the voltage at the power and ground terminals according to the manufacturer’s specifications. If the voltage is not within the expected range, repair the power or ground wire, or replace the PCM.
If the power and ground tests pass, the signal wire needs to be tested. With the connector still disconnected, use the Digital Voltmeter to measure the voltage at the signal wire terminal. The voltage should be 5 volts. If not, repair the signal wire, or replace the PCM.
If all previous tests have passed and the P0257 code persists, it is likely that the FRP sensor or Fuel Quantity Actuator has failed. However, a failed PCM cannot be ruled out until the FRP sensor or Fuel Quantity Actuator is replaced. If unsure, it is recommended to seek assistance from a trained automotive diagnostician. Note that PCMs must be programmed or calibrated to the vehicle for correct installation.
