GM Service Manual Online
For 1990-2009 cars only

With the engine running at idle and the shift lever in Neutral (N), depress the brake pedal and hold a constant foot pressure on the pedal. If the pedal gradually falls away with the constant pressure, the hydraulic system may be leaking. Check the following visually to confirm a suspected leak.

    • Master Cylinder Fluid Levels. While a slight drop in the levels occurs with normal lining wear, an abnormally low level, resulting in illumination of the BRAKE warning lamp, may mean a leak in the system. The system may be leaking internally or externally; refer to Master Cylinder for diagnosis of possible master cylinder leaks. (The system may appear to pass this test, but still have slight leakage.)
    • Brake Hose and Pipe Connections. If leakage is found, verify the torque of the fasteners and/or replace the hose or pipe.
    • Connecting Brake Components. Inspect for damage, rebuild or replace as needed.
    • Caliper and Wheel Cylinder Boots. If leakage is found, rebuild or replace the assembly as specified in Front Disk Brake Caliper or Drum Brake.

Also, check the service brake pedal travel, the brake adjustment and the parking brake adjustment.