Fuel Level Sensor: Description and Operation

The fuel level sender is a ceramic card assembly that consists of the float, the wire float arm, and the rheostat. The fuel level is sensed by the position of the float and float arm, which operates the rheostat.

The rheostat is mounted on the fuel sender and located in series with the voltage supply circuit from the fuel gauge. As the position of the float varies with fuel level, the rheostat produces a variable resistance between the fuel gauge. The fuel gauge converts this variable resistance into the fuel level reading display on the instrument panel.

An isolated circuit is used in this application. The isolated ground circuit uses a dedicated ground wire from the rheostat to the fuel sender connector. The isolated ground circuit is used to prevent erratic fuel level readings caused by a difference in voltage potential among vehicle ground points. An isolated ground terminal is connected electrically to one end of the ceramic card.