Circuit Description

The fuel level sensor is an important input to engine control module (ECM) for the enhanced evaporative system diagnostic. Fuel level information is needed for the ECM to know the volume of fuel in the tank. The fuel level affects the rate of change in air pressure in the evaporative system.

The sending unit is a float in the fuel tank which moves a wiper arm across a variable resistor. Low fuel level causes high resistance in the sending unit, and this is recognized by the ECM because the circuit operates at a corresponding high voltage.