Fuel Level Sending Unit
WARNING: This page is about a different car, the 2007 Chrysler PT Cruiser. However, it is still accessible from the selected car via links, so may be relevant.
Its resistance changes with the amount of fuel in the tank. The float arm attached to the sensor moves as the fuel level changes.
The fuel level input is used as an input for OBD II. If the fuel level is below 15% or above 85% of total tank capacity several monitors are disabled. There are diagnostics for the level circuit open and shorted.