VALVE, One Way Check: Operation: Operation
WARNING: This page is about a different car, the 2010 Dodge Avenger and 2010 Chrysler Sebring. However, it is still accessible from the selected car via links, so may be relevant.
The air injection check valve (1) allows air pumped from the air injection pump to enter the exhaust manifold during cold engine starts only. Air pressure from the air injection pump causes the spring inside the air injection check valve to open allowing air to flow into the exhaust system.