Check Valve
WARNING: This page is about a different car, the 2003 Mitsubishi Outlander. However, it is still accessible from the selected car via links, so may be relevant.
CAUTION:
If check valve is defective, replace check valve and vacuum hose as a unit. DO NOT disassemble check valve.
Remove vacuum hose from power brake booster. DO NOT remove check valve from hose. Check valve should hold vacuum in one direction and allow air to pass in other direction. Negative pressure (vacuum) should be created and held when vacuum is connected on brake booster side.