Hydraulic System: Description and Operation

Hydraulic Brake Actuation

Hydraulic Brakes

The hydraulic brake actuation system consists of the following components:

- Brake master cylinder and fluid reservoir
- Brake tubes and hoses
- Brake pedal and bracket
- Hydraulic Control Unit (HCU)

The brake pedal is connected to the power brake booster, which is connected to the brake master cylinder. When the brake pedal is pressed, brake fluid is forced from the master cylinder, which distributes the fluid between the front and rear wheels, through the double-walled steel tubes and flexible hoses into two ports in the HCU. One port is for the front wheels, the other is for the rear wheels. The HCU then distributes the fluid to the individual brake calipers at each wheel. The fluid enters the caliper, forcing the caliper pistons and brake pads against the brake disc friction surface, slowing or stopping rotation of the brake disc. When the brake pedal is released, brake fluid pressure is relieved, returning the front and rear brake caliper pistons and brake pads to the unapplied position.

For information on the HCU, refer to Vehicle Dynamic Systems Description and Operation.

Adjustable Pedals

Adjustable brake and accelerator pedals are available as an optional feature on this vehicle. Brake pedal position can be changed in phase with the accelerator pedal to increase driver comfort. Two different adjustable pedal systems are available; one that is connected to the memory feature option and one that is not connected to the memory feature option.

Adjustable brake pedals consist of the following components:

- Driver Seat Module (DSM), refer to Seating Service and Repair (with memory feature only)
- Memory SET switch, refer to Seating Service and Repair (with memory feature only)
- Remote Keyless Entry (RKE) transmitter, refer to Handles, Locks, Latches and Entry Systems Description and Operation (with memory feature only)
- Adjustable brake pedal and bracket
- Adjustable accelerator pedal, refer to Acceleration Control Acceleration Control
- Adjustable pedal switch
- Adjustable pedal motor and bracket, refer to Acceleration Control Acceleration Control
- Adjustable pedal cable
- Steering Column Control Module (SCCM)
- Body Control Module (BCM) (with memory feature only)

The pedals are adjusted through the use of a rocker switch mounted on the SCCM, the memory SET switch mounted on the door trim panel or the RKE transmitter. When the adjustable pedal switch is pressed, voltage is sent to the motor which spins a cable that is attached to the adjustable brake pedal. As the cable spins, the pedals move either forward (away from the driver) or rearward (toward the driver) depending on how the switch is pressed and/or current pedal position.

The adjustable pedal switch is serviced separate from the SCCM.

With Memory Feature

When the RKE transmitter is activated, a Medium Speed Controller Area Network (MS-CAN) message is sent to the DSM. If the memory SET switch is pressed, the DSM senses continuity to ground through the switch. In either case, the DSM sends a message over the MS-CAN bus to the BCM, which acts as a gateway module and sends a message over the High Speed Controller Area Network (HS-CAN) bus to the SCCM. The SCCM then sends voltage to the adjustable pedal motor. When voltage is applied, the adjustable pedal motor spins a cable that is attached to the adjustable brake pedal. As the cable spins, the pedals move either forward (away from the driver) or rearward (toward the driver) depending on how the switch is pressed and/or current pedal position.