Principles of Operation

Principles of Operation

Hydraulic Brake System
Applying the brake pedal uses lever action to push a rod into the brake booster, which through the use of vacuum, boosts the force of the rod and then transmits this force into the master cylinder. This produces hydraulic pressure in the master cylinder.
On vehicles not equipped with ABS, the hydraulic pressure is transmitted by brake fluid through the brake tubes to the individual brake calipers. On vehicles equipped with ABS, the hydraulic pressure is transmitted by brake fluid through the brake tubes to the ABS hydraulic control unit (HCU), which then distributes that pressure to the individual brake calipers. The brake calipers and wheel cylinders use the hydraulic pressure to apply the brake pads and shoes. The application of the brake pads and shoes will cause the rotation of the wheels to slow or stop depending on how much brake pressure is applied. The parking brakes carry out the same function except that they are mechanically actuated by a cable that connects only to the rear brakes.

Red Brake Warning Indicator
The red brake warning indicator alerts the driver to certain conditions that exist in the brake system. The instrument cluster performs a bulb check when the ignition key is turned to the RUN position. The conditions that cause the indicator to illuminate are low brake fluid level, the parking brake is applied or there is a fault in the ABS module (if the yellow ABS warning indicator is also illuminated). The brake fluid level switch is part of the brake fluid reservoir and is wired directly to the smart junction box (SJB), when the fluid is below the predetermined level, the SJB sends a message to the instrument cluster along the high speed communication area network (HS-CAN) bus to illuminate the indicator. The parking brake switch is mounted on the parking brake control and is wired to the SJB. When the parking brake is engaged, the SJB sends a message to the instrument cluster along the HS-CAN bus to illuminate the indicator. When there is one or more DTCs in the ABS module, the module sends a message to the instrument cluster along the HS-CAN bus to illuminate the red brake warning indicator and the yellow ABS warning indicator.