One Way Check Valve: Operation
WARNING: This page is about a different car, the 2005 Dodge Stratus and 2005 Chrysler Sebring. However, it is still accessible from the selected car via links, so may be relevant.
The one-way check valve has a one-way diaphragm which prevents hot exhaust gases from backing up into the air injection hose and air injection pump. The check valve will protect the system if the air injection pump, an air hose ruptures or exhaust system pressure becomes abnormally high.