Theory Of Operation
WARNING: This page is about a different car, the 2024 RAM ProMaster EV. However, it is still accessible from the selected car via links, so may be relevant.
The Body Control Module (BCM) provides a reference voltage to the Brake Fluid Level Switch, through the Brake Fluid Level Signal circuit. When the brake fluid level is above the low level switch, the Brake Fluid Level Switch is opened and the reference voltage travels through an internal 1000 Ohm diagnostic resistor which is parallel to the internal Brake Fluid Level Switch. When the brake fluid level is below the low level switch, the Brake Fluid Level Switch closes and the reference voltage bypasses the diagnostic resistor.
When the BCM detects the brake fluid level is low, the BCM sends a CAN Bus message to the Instrument Cluster (IC), in order to illuminate the BRAKE warning lamp.