Theory Of Operation
WARNING: This page is about a different car, the 2014 Fiat 500e. However, it is still accessible from the selected car via links, so may be relevant.
The Radiator Coolant Temperature Sensor is a variable resistor that functions as a normal two wire 5 volt sensor. The Battery Pack Control Module (BPCM) supplies a 5 volt reference and a ground to the sensors low reference signal circuit.