Check Valve
WARNING: This page is about a different car, the 1996 Mazda Millenia. However, it is still accessible from the selected car via links, so may be relevant.
Remove check valve. See Figure . Apply air pressure to port "A" (White port) of check valve. Air should flow from port "B". Apply air pressure to port "B" (Green port) of check valve. Air should not flow from port "A". Replace check valve as necessary.