The fuel gauge sending unit (fuel level sensor) is attached to the side of the fuel pump module. The sending unit consists of a float, an arm, and a variable resistor track. The resistor track is used to send electrical signals to the PCM for fuel gauge and for OBD II emission requirements.
As fuel level increases the float and arm move up. This decreases the sending unit resistance, causing the fuel gauge to move towards "F". As fuel level decreases, the float and arm move down, and the gauge moves to "E".
When this signal is sent to the PCM, the PCM will transmit the data across the CCD bus circuits to the instrument panel. Here it is translated to an appropriate fuel gauge level reading.
For OBD II emission monitor requirements, a voltage signal is sent from the resistor track on the sending unit to the PCM to indicate fuel level. The purpose of this feature is to prevent the OBD II from recording/setting false misfire and fuel system monitor trouble codes. The feature is activated if the level in the tank is less than approximately 15 percent of its rated capacity. If equipped with a leak detection pump, this feature will also be activated if the fuel level in the tank is more than about 85 percent of its rated capacity.