Circuit Relays

Fuel pump relay No. 1 allows the fuel pump to be energized by the PCM. When the ignition is first turned "ON", the PCM energizes fuel pump relay No. 1 for two seconds. This allows the fuel pump to run for two seconds and build up fuel pressure for cranking. The PCM then waits for ignition reference pulses from the Ignition Control Module (ICM). Once the PCM sees references pulses, the PCM energizes relay No. 1 to run the fuel pump.

As a backup system to the PCM and fuel pump relay No. 1, the fuel pump can also be turned on by the oil pressure sensor through fuel pump relay No. 2. If the PCM or fuel pump relay No. 1 is faulty and the engine is cranked, the oil pressure switch contacts of the sensor will close once oil pressure is built up and energize fuel pump relay No. 2, which then runs the fuel pump.

A faulty fuel pump relay No. 1 may cause long cranking times and should set a PCM Trouble Code. A faulty fuel pump relay No. 2 will only cause a no start condition if fuel pump relay No. 1 is also disabled.