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 Body Control Module (BCM) provides a reference voltage on the brake fluid level signal circuit through a pull-up resistor. The Brake Fluid Level Switch switches the brake fluid level signal circuit to ground when the fluid level is low. A diagnostic resistor internal to the switch is placed in parallel with the switch.