Theory Of Operation
WARNING: This page is about a different car, the 2015 Fiat 500. However, it is still accessible from the selected car via links, so may be relevant.
The Electric Vehicle Control Unit (EVCU) monitors the status of both brake switches. Brake Switch 1 is normally closed and Brake Switch 2 is normally open. When the brake pedal is pressed the status of both switches change from Closed to Open or Open to Closed. If one switch status changes and the other does not a diagnostic code will set.