Theory Of Operation

The Brake System Control Module (BSCM)  performs diagnostic using Brake Travel Percentage, Brake Pedal Pressure and Brake Torque signal and rationalize them. The BSCM then sends the messages to the PCM through the CAN Bus.

The Brake Travel Percentage  signal is the average of two sensors hard wired internal to the Brake System Control Module (BSCM). The BSCM broadcasts the Brake Travel Percentage signal information over the CAN Bus. When both sensors are good PCM receives average of two sensors. If one of the sensor fails, PCM receives the sensor signal deemed to be valid by BSCM. If both sensors fail, BSCM will set an Signal Not Available (SNA) state on the Brake Travel Percentage signal. PCM does not take any default action when one brake travel sensors fail in the BSCM. The BSCM should set a fault. The PCM receives only one signal from the BSCM and assumes the signal is correct.

The Brake Pedal Pressure  signal is utilized to support Brake Pedal Pressure Rationality. Autonomous braking systems such as Active Cruise Control (ACC) have the potential to defeat the Brake Pedal Position Rationality diagnostic as the vehicle can be brought to a complete stop without depressing the Brake Pedal, thus false failing the rationality. The Brake Pedal Position Rationality needs the Brake Pedal Pressure Signal to determine if any autonomous braking system is active. The Brake Pedal Pressure only measures the brake system pressure applied by the vehicle operator and is not affected by BSCM, parking brake or autonomous braking systems. Brake Pedal Pressure signal information is sent to the PCM over the CAN Bus. The Brake Pedal Pressure is internal to the Brake System Control Module (BSCM).

The Brake Torque (BT)  signal is a calculated measurement of braking force as determined by the BSCM. The Brake Torque signal is used as a third correlating signal for Brake Pedal Position Rationality diagnostics and is accurate during both vehicle operator braking, as well as autonomous braking events.