Fuel Pump Relay: Description and Operation
PURPOSEWhen the ignition switch is turned to the "ON" position (before engaging starter), the Powertrain Control Module (PCM) energizes the fuel pump relay for two seconds causing the fuel pump to pressurize the fuel system.
OPERATION
If the PCM does not receive ignition reference pulses (engine cranking or running) within two seconds, it shuts "OFF" the fuel pump relay, causing the fuel pump to stop.
As a backup system to the fuel pump relay the fuel pump also can be energized by the fuel pump switch and engine oil pressure sensor. The sensor has two internal circuits. One operates the oil pressure indicator or gauge on the instrument cluster, and the other is a normally open switch which closes when oil pressure reaches about 28 kPa (4 psi). If the fuel pump relay fails, the fuel pump and engine oil pressure indicator 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 switch and engine oil pressure indicator switch energizes the fuel pump as soon as oil pressure reaches about 28 kPa (4 psi).