GM Service Manual Online
For 1990-2009 cars only

Inspect the hydraulic brakes system for leaks by performing the following steps:

  1. Run the engine at idle with the shift lever in neutral.
  2. Press the brake pedal. Hold constant pressure on the pedal.
  3. If the pedal gradually falls away while under constant pressure, the hydraulic system may be leaking. Perform a visual inspection in order to confirm any suspected leak.
  4. Inspect the master cylinder fluid level. A slight drop in the reservoir level does result from lining wear. However, an abnormally low fluid level in either reservoir may indicate an internal or external leak. The system may appear to pass this inspection, but still have a slight leak.
  5. If the fluid level is normal, inspect for external leaks in the following areas:
  6. • The brake pipe
    • The hose connections
    • The caliper
    • The wheel cylinder boots
  7. Inspect the following actions:
  8. • The service brake pedal travel
    • The brake adjustment
    • The parking brake adjustment