Technical Description of OBD-II Trouble Code
The code P0258 refers to the Injection Pump Fuel Metering Control B Low (Cam/Rotor/Injector). It is a generic powertrain/engine diagnostic trouble code that can apply to diesel fueled OBD-II equipped engines in various vehicles, including Mercedes Benz and VW. 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. This circuit consists of a Fuel Rack Position (FRP) Sensor and a Fuel Quantity Actuator.
The FRP sensor converts the amount of diesel fuel delivered by the Fuel Quantity Actuator to the injectors into an electrical signal for the Powertrain Control Module (PCM). The PCM uses this voltage signal to determine the appropriate amount of fuel to put into the engine based on its operating conditions. If the input from the FRP sensor does not match the normal engine operating conditions stored in the PCM’s memory, even for a brief moment, the P0258 code is set. The PCM also checks the voltage signal from the FRP sensor during the initial Key On.
The P0258 code is triggered when the voltage at the FRP sensor stays below a set level (usually under 0.3V) for an extended period of time. This code is typically associated with an electrical circuit issue. To determine the specific “B” part of the circuit for your vehicle, refer to a vehicle-specific repair manual.
The severity of this DTC is considered to be not severe because the PCM can compensate adequately for the electrical failure.
Symptoms of the Code
Some symptoms of a P0258 trouble code may include:
Common Causes of the Code
Some common causes of the P0258 code may include:
Troubleshooting Steps for P0258
Here are some troubleshooting steps for the P0258 code:
1. Check for technical service bulletins (TSB) for your vehicle to see if there is a known issue with a known fix provided by the manufacturer.
2. Locate the FRP sensor on your vehicle, which is usually found inside or on the side of the injection pump bolted to the engine. Inspect the connector and wiring for any signs of damage such as scraping, rubbing, bare wires, burn spots, or melted plastic. Carefully inspect the terminals inside the connector 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.
3. If you have a scan tool, clear the diagnostic trouble codes from memory and see if the P0258 code returns. If it does not, the issue was likely due to the connections.
4. If the P0258 code does return, you will need to test the FRP sensor and its associated circuits. With the Key Off, disconnect the electrical connector at the FRP sensor. Connect a Digital Voltmeter black lead to the ground terminal at the FRP sensor wiring harness connector, and connect the red lead of the Digital Voltmeter to the power terminal. Turn the Key On Engine Off and check the voltmeter reading according to the manufacturer’s specifications (either 12 volts or 5 volts). If the reading is not correct, repair the power or ground wire, or replace the PCM.
5. If the power test passed, you will need to test the signal wire. With the connector still disconnected, move the red lead of the voltmeter from the power wire terminal to the signal wire terminal. The voltmeter should read 5 volts. If not, repair the signal wire, or replace the PCM.
6. If all prior tests have passed and the P0258 code persists, it is likely that the FRP sensor / Fuel Quantity Actuator has failed. However, a failed PCM cannot be ruled out until the FRP sensor / Fuel Quantity Actuator is replaced. If unsure, seek assistance from a trained automotive diagnostician. Note that PCMs must be programmed or calibrated to the vehicle for correct installation.
