Fuel Pump: Description and Operation

FUEL PUMP CIRCUIT
Start Up
When the ignition switch is turned to the "ON" position (before engaging starter), the Powertrain Control Module (PCM) energizes the fuel pump relay for a calibrated time (approximately 2 seconds). This builds up fuel pressure quickly. If the engine is not started within two seconds, the PCM shuts "OFF" the fuel pump and waits until ignition reference pulses are present. As soon as the engine is cranked, the PCM energizes the relay which powers the fuel pump..

Backup Operation
As a backup system to the fuel pump relay, the fuel pump also can be energized by the fuel pump and engine oil pressure switch. The fuel pump and engine oil pressure indicator switch is a normally open switch that closes when oil pressure reaches about 28 kPa (4 psi). If the fuel pump relay fails, the fuel pump and engine oil pressure switch powers the fuel pump.