The fuel pump relay is a type of switch that turns power on and off to your vehicle’s fuel pump. The pump itself needs a significant amount of power to operate, so, like many other electrical components, it is connected to the 12 volt electrical system. But the signal from the engine control module (ECU, the computer that controls engine function) is a low-voltage electrical signal, far too low to switch the higher-voltage pump. Therefore, a relay is used instead.
The ECU sends a low-voltage signal to the fuel pump relay which, in turn, switches on the high-voltage circuit for the fuel pump. This arrangement allows for sufficient power to operate the pump without damaging sensitive electronic equipment. The fuel pump relay turns on when you turn the key in the ignition and continues to allow power to the fuel pump whenever the engine is running. Internally, the relay is made up of an electromagnet that is energized by the ECU signal and that pulls a high-voltage contact closed to power up the fuel pump.