Fuel Pump Relay: Description and Operation

Fuel Pump Relay:

PURPOSE
To activate the fuel pump

OPERATION
When the ignition switch is turned to the "ON" position (engine not running), the Engine Control Module (ECM) turns the fuel pump relay "ON" for two seconds, causing the fuel pump to pressurize the fuel system. If the ECM 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 turned "ON" by the oil pressure sensor/switch. The oil pressure sender has two internal circuits. One operates the oil pressure indicator or gauge in 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, a Code 54 will be set in the ECM and the 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 oil pressure switch turns "ON" the fuel pump as soon as oil pressure reaches about 28 kPa (4 psi).