How a Fuel Pump Works

Here's what's inside the fuel pump and how it works on your car.

The fuel pump, or fuel sender unit, is responsible for sending pressurized fuel to the fuel rail on the engine. It is normally situated inside the gas tank, cooled by surrounding fuel.

The fuel pump assembly consists of an electric DC motor with a paddle, a pickup screen, float, tank level sensing unit, filter, pressure regulator as well as the empty level sensor.

The DC motor drawings fuel through a turning paddle in through the housing of the motor, past the rotors and brushes out the top.

Fuel then saturates the filter, where it can then make its way up the top to the fuel line leading to the engine. Excess pressure built up in the filter is bled off through a pressure regulator valve at the bottom of the assembly, where the fuel is returned to the tank.

The tank float attaches to an arm that attaches to a metal head. The head moves in a semi circular pattern against a circuit board with printed resistors. The measured resistance values are relayed back to the instrument cluster to determine fuel amount.

The empty level sensor is a device that looks like a resistor. When submerged in fluid, it reads 2K ohms. When dry, it reads an open circuit and turns the light on the dashboard warning of low fuel in the tank.

Assembly of these components are held together by plastic pieces which are clipped together. Often these require disassembly when replacing defective pump units, as only the motor needs to be replaced.

The fuel pump in this video was removed from a 2001 Toyota Corolla.


Replacement fuel pump motors can be found here: https://amzn.to/2xuDpmr
A basic metric socket set is all you need to access it: https://amzn.to/32cEhKm
If you are having issues with fuel pressure, check it using this tool from OTC: https://amzn.to/2xynzHi

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