Fuel Pump Electrical Circuit

When the ignition switch is turned to the "ON" position (engine not running), the ECM energizes the fuel pump relay 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 energized by the fuel pump and engine oil pressure indicator switch. The switch has two internal circuit. One operates the oil pressure indicator or gage in the instrument cluster, and the other is a normally open switch which closes when oil relay fails, a Diagnostic Trouble Code (DTC) 54 is set in the ECM, and 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 and engine oil pressure indicator switch energizes the fuel pump as soon as oil pressure reaches about 28 kPa (4 psi).