C 1500 Truck 2WD V6-4.3L VIN W (1996)
Oil Pressure Switch (For Fuel Pump): Testing and Inspection
Fuel Pump Electrical Circuit Description
Fuel Pump Electrical Circuit
When the ignition switch is turned to the ON position (before engaging the starter), the VCM energizes the fuel pump relay for 2 seconds causing the
fuel pump to pressurize the fuel system. If the VCM does not receive the ignition reference pulses (engine cranking or running) within 2 seconds, the
control module shuts off the fuel pump relay, causing the fuel pump to stop.
As a backup system to the fuel pump relay, the fuel pump oil pressure switch can energize the fuel pump. The switch has 2 internal circuits. One circuit
operates the oil pressure indicator or gage in the instrument cluster. The other circuit is a normally open switch which closes when the oil pressure
reaches about 28 kPa (4 psi). If the fuel pump relay fails, the fuel pump oil pressure switch runs the fuel pump.
An inoperative fuel pump relay can result in long cranking times, particularly if the engine is cold. The fuel pump oil pressure switch energizes the fuel
pump as soon as oil pressure reaches about 28 kPa (4 psi).
