Secondary AIR Diverter Valve
WARNING: This page does not describe the selected car, but rather 32 other vehicles, including the 2009 Mercury Mountaineer, 2009 Mercury Milan, 2009 Mercury Mariner, 2009 Mercury Grand Marquis, and 2009 Lincoln Town Car. However, it is still accessible from the selected car via links, so may be relevant.
The secondary AIR diverter valve is used with the secondary AIR pump to provide on/off control of air to the exhaust manifold and catalytic converter. When the secondary AIR pump is on and vacuum is supplied to the AIR diverter valve, air passes the integral check valve disk. When the secondary AIR pump is off, and vacuum is removed from the AIR diverter valve, the integral check valve disk is held on the seat and stops air from being drawn into the exhaust system and prevents the back flow of the exhaust into the secondary AIR system.