GM Service Manual Online
For 1990-2009 cars only
  1. Run the engine at idle.
  2. Shift the gear lever into NEUTRAL.
  3. Depress the brake pedal and hold the pedal with a constant foot pressure.
  4. If the pedal gradually falls away with the constant pressure, the hydraulic system may be leaking. Perform the following visual inspection in order to confirm any suspected leak:
  5. 4.1. Inspect the master cylinder fluid levels. Normal lining wear may cause a slight drop in the reservoir level. An abnormally low level in either reservoir may indicate a leak in the system. The hydraulic system may be leaking either internally or externally. Refer to Master Cylinder Diagnosis . The system may appear to pass this test but still have slight leakage.
    4.2. Verify that the brake fluid level is normal and that no leaks are present at the following locations:
       • The brake pipes
       • The hose connections
       • The caliper
       • The wheel cylinder boot
    4.3. Inspect the following components if any leakage is found:
       • The brake pedal travel
       • The brake adjustment
       • The parking brake adjustment