Fuel Pump Relay & Fuel Pump Resistor

Fuel pump speed is controlled at low speed or high speed depending on if engine is cranking or engine load. When engine is cranking and start signal is delivered to Engine Control Module (ECM), the circuit opening relay ground circuit is grounded at ECM terminal FC. Circuit opening relay then provides full battery voltage to fuel pump relay. Fuel pump relay delivers full battery voltage to fuel pump and fuel pump operates at high speed. When start signal is released and engine is idling or under light load, ECM then grounds the fuel pump relay at ECM terminal FPR. Fuel pump relay closes and provides voltage through the fuel pump resistor to the fuel pump. Fuel pump now operates at low speed.