Fuel Pump Ballast Resistor Relay: Description and Operation

Fuel Pump Relay And Resistor Circuit Schematic:

The Fuel Pump Relay, mounted on the RH side of the engine compartment, controls the speed of the fuel pump based on intake air volume and engine rpm. When the Circuit Opening Relay sends power from terminal FP, the ECU grounds terminal FPR and sends current to the fuel pump through the fuel pump resistor. This causes a supply voltage drop, slowing the fuel pump speed slightly. When engine conditions dictate (under ECU control), the ground from the ECU is interrupted and unresisted battery current is sent to the fuel pump via terminal FP. Fuel pump speed is increased with the increase in voltage.