GM Service Manual Online
For 1990-2009 cars only
  1. With the engine running at idle, depress the brake pedal.
  2. Hold the brake pedal using constant pressure.
  3. If the pedal gradually falls away while using constant pressure, the hydraulic system may be leaking.
  4. If a leak is suspected, perform the following visual inspection in order to confirm any suspected leak:
  5. 4.1. Inspect the master cylinder reservoir brake fluid level. A slight drop in level occurs with normal pad and lining wear. An abnormally low level, resulting in illumination of the BRAKE indicator, may indicate a leak in the system. The system may be leaking internally or externally.
    4.2. Inspect for a cracked master cylinder casting or for brake fluid around the master cylinder. Leaks are indicated only if there is at least a drop of fluid. A damp condition is not abnormal.
    4.3. Inspect for leaks at the brake pipe and the brake hose connections. If leakage is found, complete the following steps:
       • Verify the torque of the fasteners.
       • Replace the pipe or the hose.
    4.4. Inspect the connecting brake components for damage. Repair or replace the components as necessary.
    4.5. Inspect the caliper and the wheel cylinder boots for leakage. If leakage is found, repair or replace the assembly. Refer to the appropriate procedures:
       •  Brake Caliper Replacement in Disc Brakes
       •  Brake Caliper Overhaul in Disc Brakes
       •  Wheel Cylinder Replacement in Drum Brakes
       •  Wheel Cylinder Overhaul in Drum Brakes