Vacuum Brake Booster: Testing and Inspection

FUNCTION TEST
1. With engine turned off, depress brake pedal several times, then depress brake pedal hard and hold for 15 seconds. If brake pedal sinks, a brake line, wheel cylinder or master cylinder is faulty. Repair or replace as necessary.
2. Start engine with brake pedal depressed. Pedal should sink slightly. If it does not, the booster or check valve is faulty. Repair or replace as necessary.

LEAK TEST
1. Depress brake pedal with engine running, then stop engine and hold brake pedal for 30 seconds. Pedal height should not vary. If it does, the booster is faulty. Repair or replace as necessary.
2. With engine turned off, depress brake pedal several times using normal pressure. When pedal is first depressed, it should be low, then with every consecutive application pedal height should rise. If it does not rise, check booster check valve.

CHECK VALVE TEST
1. Disconnect brake booster vacuum hose at booster.
2. Start engine and let idle. Vacuum should exist at hose end. If vacuum does not exist, the check valve is not working properly. Replace check valve and retest.