For 1990-2009 cars

With the engine running at idle, press the brake pedal and hold with constant pressure.

If the pedal gradually falls away with this constant pressure, the hydraulic system may be leaking.

Perform the following visual checks to confirm any suspected leak:

1. Check the master cylinder reservoir brake fluid level. While 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.
2. Check 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 normal.
3. Check for leaks at the brake pipe and brake hose connections. If leakage is found, verify the torque of fasteners and/or replace the pipe or hose.
4. Inspect the connecting brake components for damage, and rebuild or replace as necessary.
5. Check the caliper and wheel cylinder boots for leakage. If leakage is found, rebuild or replace the assembly. For service procedures, refer to Brake Caliper Replacement in Disc Brakes or to Wheel Cylinder Replacement in Drum Brakes.