Hose and Check Valve

WARNING: This page is about a different car, the 2007 Ford Ranger. 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 of the power brake booster.
is positioned between the power brake booster and the power brake booster hose.
closes when the engine is turned OFF.
traps engine vacuum in the power brake booster when in the closed position.
retains vacuum to provide 2-3 power-assisted brake applications with the engine off.