Fuel Pump Relay: Description and Operation

Component View:

The L67 engine utilizes a two speed fuel pump speed control relay. When the ignition switch is first turned ON, the PCM energizes the fuel pump relay which applies power to the fuel pump through the fuel pump speed control relay. The fuel pump relay will remain ON as long as the engine is running or cranking and the PCM is receiving reference pulses. If no reference pulses are present, the PCM de-energizes the fuel pump relay within 2 seconds after the ignition is turned ON or the engine is stopped. The fuel pump delivers fuel to the fuel rail and injectors, then to the fuel pressure regulator. The fuel pressure regulator controls fuel pressure by allowing excess fuel to be returned to the fuel tank. With the engine stopped, the fuel pump can be turned ON by using the scan tool output controls function.

The PCM alters fuel pump speed by energizing the fuel pump speed control relay. Under most conditions, the fuel pump speed control relay is energized. The applied voltage to the fuel pump is controlled by a resistor assembly. When higher fuel volume is required due to increased engine load (MAP sensor value over 90 kPa), the PCM de-energizes the fuel pump speed control relay circuit. The increased voltage to the in tank fuel pump allows a higher volume of fuel to be delivered to the fuel rail. The PCM also compensates for low system voltage by de-energizing the fuel pump speed control relay circuit. Refer to Fuel Pump Relay Circuit Diagnosis for further information and diagnosis.