When ignition switch is turned to ON position, PCM/VCM turns electric fuel pump on by energizing fuel pump relay. PCM/VCM keeps relay energized if engine is running or cranking (PCM/VCM is receiving reference pulses from ignition module). If there are no reference pulses, PCM/VCM turns pump off within 2-20 seconds after key on.
As a back-up system to fuel pump relay, the oil pressure switch also activates fuel pump. The oil pressure switch is normally open until oil pressure reaches about 4 psi (.28 kg/cm2 ). If fuel pump relay fails, the oil pressure switch closes when oil pressure is obtained and operates the fuel pump.
Cranking time will be longer if fuel pump does not receive current until oil pressure switch contacts close.
Oil pressure switch may be combined into a single unit with an oil pressure gauge sending unit or sensor.
PCM/VCM monitors fuel pump circuit between fuel pump relay/oil pressure switch and fuel pump, enabling PCM/VCM to determine if fuel pump is being energized by fuel pump relay or oil pressure switch. A failure in this monitored circuit results in the setting of a related diagnostic trouble code in PCM/VCM memory.
Friday, February 4th, 2011 AT 1:57 AM