With the engine running at idle, press the brake pedal and hold the pedal 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. Inspect the master cylinder reservoir brake fluid level. A slight drop in the brake fluid level occurs with normal pad and lining wear. However, an abnormally low level, resulting in the illumination of the BRAKE indicator, may indicate an internal or external leak in the system.
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.
3. Inspect for leaks at the brake pipe and the brake hose connections. If leakage is found, verify the torque of the fasteners or replace the pipe or hose.
4. Inspect the connecting brake components for damage, and rebuild or replace the components as necessary.
5. Inspect the caliper and the wheel cylinder boots for leakage. If leakage is found, repair or replace the assembly. For service procedures, refer to Brake Caliper Replacement in Disc Brakes or to Wheel Cylinder Overhaul in Drum Brakes.
6. Inspect for leaks at the brake pressure modulator valve (BPMV). If leakage is found replace or repair the assembly. Refer to Brake Pressure Modulator Valve Replacement in Antilock Brake System.