S15/T15 Sonoma P/U 2WD L4-2.2L VIN 4 (1995)
Fuel Pump Relay: Description and Operation
OPERATION
When 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 allowing the fuel pump to pressurize the fuel system. If the PCM does not receive ignition reference pulses (engine cranking
or running) within two seconds, it de-energizes the fuel pump relay, causing the fuel pump to stop.
As a backup system to the fuel pump relay, the fuel pump can be energized by the fuel pump and engine oil pressure indicator switch. The switch
has two internal circuits. One operates the oil pressure indicator or gage 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, the fuel pump and engine oil pressure indicator switch runs the
fuel pump.
An inoperative fuel pump relay can result in long cranking times. The fuel pump and engine oil pressure indicator switch energizes the fuel pump
as soon as oil pressure reaches about 28 kPa (4 psi).
