Hydraulic System: Description and Operation

Substandard or Contaminated Brake Fluid
Improper fluid, water, or any other contaminants in the brake fluid may cause the brake fluid to boil or deteriorate rubber components in the hydraulic system.

Swollen master cylinder piston seals show that rubber deterioration has occurred. Deterioration may also be shown by the swelling of wheel cylinder boots, caliper boots, or the master cylinder reservoir diaphragm.

If rubber deterioration is found, replace all rubber parts in the system, including the hoses. Check for fluid on the brake linings. If any is found, replace the linings.

If the fluid is contaminated and the master cylinder piston seals are satisfactory, check for leaks or excessive heat conditions. If no leaks or excessive heat conditions are found, flush the system.

Flushing the System
Flushing the brake hydraulic system involves running new brake fluid through the system until the fluid at each bleeder.valve comes out clear. This is the only way to clean contaminated fluid out of the system.

The brake hydraulic system should be flushed with clean brake fluid any time new parts are installed. Flushing is also recommended if there is any question of contamination, the grade of fluid in the system, or of mineral oil in the fluid.

Circuit Description

Battery voltage is supplied to the Brake Indicator through the GAUGES Fuse and the PNK (39) wire when the Ignition Switch is in RUN or START. Ground is provided through the TAN/WHT (33) and LT BLU (1134) wire by the Park Brake Warning Switch, Brake Pressure Warning Switch or the TAN/WHT (33) and PPL (680) and the Brake Pressure Modulator Valve (BPMV).

The Park Brake Warning Switch closes when the Parking Brake is applied. The Brake Indicator lights to alert the driver.

The Brake Pressure Warning Switch closes to light the BRAKE Indicator when there is low brake fluid pressure in one of the two hydraulic brake systems. This could be caused by a leak in one of the brake lines.

The 2.2 L Engine's Electronic Brake Control Module (Part of the Brake Pressure Modulator Valve) or the 4.3 L Engines Vehicle Control Module grounds the BRAKE Indicator when the module senses certain malfunctions in the hydraulic portion of the system. The module grounds the ANTILOCK Indicator when the module senses a malfunction in the electrical or electronic portion of the system. Brake voltage input is supplied to the module through the TCC Brake and Cruise Control Release Switch whenever the brakes are applied.