Hose and Check Valve

WARNING: This page is about a different car, the 2006 Mercury Grand Marquis and 2006 Ford Crown Victoria. However, it is still accessible from the selected car via links, so may be relevant.

The power brake booster check valve:

is located on the front shell of the power brake booster.
is positioned between the power brake booster and the power brake booster vacuum hose.
closes when the engine is turned OFF.
in the closed position, traps engine vacuum in the power brake booster.
retains vacuum to provide several power assisted brake applications with the engine OFF.