The injection pump control circuit “A” can be located inside, on the side, or built into the injection pump. This circuit is comprised of the Fuel Rail Pressure (FRP) Sensor and a fuel quantity actuator.
The FRP sensor converts the amount of diesel fuel delivered by the actuator into an electrical signal. This information is then sent to the Powertrain Control Module (PCM), which uses it to determine the amount of fuel to be placed in the engine according to the engine’s operating conditions.
If the input does not match the normal operating conditions of the engine, which are stored in the memory of the PCM, the fault code P0251 OBDII is set.