Functional Test
- Start engine. Turn ignition off. Depress brake pedal several times. Depress pedal firmly and hold pressure for 15 seconds. If pedal sinks, master cylinder, brakeline or wheel cylinder is faulty.
- With pedal depressed, start engine. If pedal sinks slightly, vacuum unit is working properly. If pedal height does not vary, booster or check valve is faulty.
- With engine running, depress brake pedal lightly. Apply just enough pressure to hold back automatic transmission creep. If brake pedal sinks more than 1" (25 mm) in 3 minutes, master cylinder is faulty. Slight change in pedal height when A/C compressor cycles on and off is normal.