Note. For circuit reference, see DTC P0231 schematic.
Circuit Description
Fuel pump is powered by fuel pump relay. PCM energizes the fuel pump relay for 2 seconds at ignition on, to provide fuel pressure for starting. After the 2 second fuel pump prime, PCM will not power fuel pump until 4X reference pulses are received, indicating that the engine is cranking or running. PCM monitors voltage in the fuel pump feedback circuit to select fuel pump voltage supply faults. DTC will set when PCM sees the fuel pump is not energized (2 volts or less on feedback) with engine cranking or running.