Fuel Pump Relay: Description and Operation

When the ignition key is first turned to the "ON" position, the ECM/PCM will energize the fuel pump relay for two seconds. This increases fuel pressure for cranking. If the engine is not running within two seconds, the ECM/PCM will shut off the relay and wait until the engine starts. As soon as the engine is cranked, the ECM/PCM will energize the relay and power the fuel pump. As a backup system to the fuel pump relay, the fuel pump can also be turned "ON" by the oil pressure switch. The oil pressure switch is a normally open switch which closes when oil pressure reaches about 28 kPa (4 psi). If the fuel pump relay fails, the oil pressure switch will close and run the fuel pump.