What does it mean?
OBD II fault code P0258 is defined as “Injection Pump Fuel Metering Control “B” Low (Cam/Rotor/Injector)”, and is set when the PCM (Powertrain Control Module) detects a variation between the signal voltage delivered to the electronic fuel control actuator, and the signal voltage returned by the fuel metering control sensor. Note that this code applies to diesel engines exclusively. “B” refers specifically to the control circuit of the fuel control actuator on the pressure pump.
This is the device that controls the amount of fuel that enters the pump. “A” codes are more relevant to the same electrical issues on the pressure sensor on the fuel rail that generates the signal voltage that regulates pulse width and injection timing. All common rail diesel injection systems use a device known as an “electronic fuel control actuator” to meter the amount of fuel that is allowed to enter the actual pumping chamber(s) of a high pressure diesel fuel pump.
This device therefore determines the amount and pressure of the fuel that is ultimately delivered to the fuel rail. However, the pressure in the fuel rail needs to be controlled within a very narrow range: there are various ways in which this is accomplished, but to ensure that the actual pressure in the fuel rail closely matches the nominal design pressure, most applications use a variable resistance-type sensor to communicate the actual pressure to the PCM.
The pressure sensor converts fuel pressure into a signal voltage, which the PCM uses to calculate injector pulse width (measured in milliseconds) and injection timing (measured in degrees Before Top Dead Center) to ensure that the correct amount of fuel is injected into the cylinders under all operating conditions.
Thus, the signal voltages of the electronic fuel control actuator and the fuel metering control sensor must be in agreement for the PCM to be able to calculate an appropriate fuel delivery strategy to ensure efficient engine operation under all engine speeds and loads. On some applications, code P0258 will set and a warning light be triggered after a single failure, while on others, several failure cycles are required before the code is set and warning light is illuminated.
The image below shows a simplified schematic of a typical fuel pressure control system. Note the location of the fuel control actuator on the high pressure pump, and the location of the pressure sensor on the fuel rail. Note also that although this particular system employs an electric lift pump in the fuel tank, not all applications are so equipped.
Note: Circuit Low Input codes are often the result of low battery voltages (that can have many possible causes), bad connections across electrical connectors or previously repaired wiring, as well as corrosion in electrical connectors.
Other possible causes of low input voltages include poor installation of aftermarket components, poor quality aftermarket components like fuses, relays, and switches, and modification of the electrical system that could include the use of conductors that are not rated for use in a particular application. However, poor connections often result in high resistances in some parts of the circuit, which is why it is important to perform resistance and continuity checks during the diagnostic procedure.