Hydraulic System: Description and Operation

Brake Fluid and Brake Fluid Handling

Caution: Brake fluid may irritate eyes and skin. In case of contact, take the following actions:
^ Eye contact-rinse thoroughly with water.
^ Skin contact-wash with soap and water.
^ If ingested-consult a physician immediately.

Caution: Use only Delco Supreme 11, GM P/N 12377967, or equivalent DOT 3 brake fluid from a clean, sealed container. Do not use fluid from an open container that may be contaminated with water. Improper or contaminated fluid could result in damage to components, or loss of braking, with possible injury.

Notice: When filling the master cylinder, use only Delco Supreme 11, GM P/N 12377967, or equivalent DOT 3 brake fluid. Do not use a container that has been used for petroleum based fluids, or a container which is wet with water. Petroleum based fluids will cause swelling and distortion of rubber parts in the hydraulic brake system, and water will mix with brake fluid, lowering the boiling point. Keep all fluid containers capped to prevent contamination.

Notice: Brake fluid will damage electrical connections and painted surfaces. Use shop cloths, suitable containers, and fender covers to prevent brake fluid from contacting these areas. Always re-seal and wipe off brake fluid containers to prevent spills.

Notice: Avoid spilling brake fluid on any of the vehicle's painted surfaces, wiring, cables or electrical connectors. Brake fluid will damage paint and electrical connections. If any fluid is spilled on the vehicle, immediately flush the area with water to minimize the potential for damage.

Notice: Power steering fluid, engine oil, brake fluid, or any mineral based fluids cannot be mixed. If brake seals contact power steering fluid or steering seals contact brake fluid, seal damage will result.

Important:
^ Do not reuse the brake fluid collected during the hydraulic brake system bleeding.
^ Always store brake fluid in a closed container.
^ Reseal brake fluid containers immediately after use.
^ Do not use brake fluid left in an open container.
^ Do not use brake fluid left in an improperly sealed container.
^ Do not use the following fluids in the hydraulic brake system:
- Power steering fluid
- Automatic transmission fluid
- DOT 5 silicone hydraulic brake fluid

Brake Warning System Description and Operation

Brake Warning Indicator
The instrument panel cluster (IPC) illuminates the brake warning indicator when one or more of the following occurs:
^ The body control module (BCM) detects that the park brake is engaged. The IPC receives a class 2 message from the BCM requesting illumination.
^ The electronic brake control module (EBCM) detects a low brake fluid condition. The IPC receives a class 2 message from the EBCM requesting illumination.
^ The EBCM detects an ABS malfunction that disables dynamic rear proportioning (DRP). The IPC receives a class 2 message from the EBCM requesting illumination.
^ The IPC performs the bulb check at the start of each ignition cycle. The brake warning indicator illuminates for approximately 3 seconds before turning OFF.
^ The IPC detects a loss of class 2 communications with the BCM or with the EBCM.

Hydraulic Brake System Description and Operation

System Component Description
The hydraulic brake system consists of the following:
Hydraulic Brake Master Cylinder Fluid Reservoir: Contains supply of brake fluid for the hydraulic brake system.
Hydraulic Brake Master Cylinder: Converts mechanical input force into hydraulic output pressure. Hydraulic output pressure is distributed from the master cylinder through two hydraulic circuits, supplying front-rear opposed wheel apply circuits.
Hydraulic Brake Pressure Balance Control System: Regulates brake fluid pressure delivered to hydraulic brake wheel circuits, in order to control the distribution of braking force. Pressure balance control is achieved through a combination valve.
Hydraulic Brake Pipes and Flexible Brake Hoses: Carries brake fluid to and from hydraulic brake system components.
Hydraulic Brake Wheel Apply Components: Converts hydraulic input pressure into mechanical output force.

System Operation
Mechanical force is converted into hydraulic pressure by the master cylinder, regulated to meet braking system demands by the pressure balance control system, and delivered to the hydraulic brake wheel circuits by the pipes and flexible hoses. The wheel apply components then convert the hydraulic pressure back into mechanical force which presses linings against rotating brake system components.

Brake Assist System Description and Operation

System Component Description
The brake assist system consists of the following:
Brake Pedal: Receives, multiplies and transfers brake system input force from driver.
Brake Pedal Pushrod: Transfers multiplied input force received from brake pedal to brake booster.
Hydraulic Brake Booster: Uses power steering fluid pressure to decrease effort required by driver when applying brake system input force. When brake system input force is applied, pressurized power steering fluid is admitted to the rear of an apply piston, providing a decrease in brake pedal effort required. When input force is removed, pressurized power steering fluid is blocked off from the piston.
Power Steering System: Supplies pressurized power steering fluid used by hydraulic brake booster to decrease brake pedal effort.

System Operation
Brake system input force is multiplied by the brake pedal and transferred by the pedal pushrod to the hydraulic brake master cylinder. Effort required to apply the brake system is reduced by the hydraulic brake booster.