The Fuel Level Sensor (FLS) is located in the fuel tank, and is usually integrated in the fuel pump module.
It has a float that is connected to the arm that is mobilized by a resistor that is grounded to the fuel tank, or in some cases it may have a ground circuit dedicated to it. The voltage that is supplied to you just like the earth, changes according to the level of fuel. In general, the voltage is 5 volts.
When changing the fuel level, the float moves the arm and the resistance to ground changes, causing the voltage signal to change. This signal is sent to the fuel pump module who monitors the resistance to ground and then transmits the information to the Power Train Control Module (PCM). If this signal is greater than 5 volts for a specific time, the DTC code P0463 OBD2 is set.