Booster Check Valve Test
Disconnect brake booster vacuum hose at booster. Check valve is built into hose. See Fig 1 . Start engine, and let it idle. There should be vacuum available. If no vacuum is available, check valve is not working properly. Replace brake booster vacuum hose and check valve, and retest.
Start engine, and pinch brake booster vacuum hose between check valve and booster. Turn engine off and wait 30 seconds. Press brake pedal several times using normal pressure. When pedal is first pressed, it should be low. On consecutive applications, the pedal height should gradually rise. If pedal position does not vary, replace brake booster. If pedal position varies, replace brake booster vacuum hose/check valve assembly.