Secondary Air Injection System: Description
WARNING: This page does not describe the selected car, but rather 31 other vehicles, including the 2003 Mercury Sable, 2003 Mercury Mountaineer, 2003 Mercury Marauder, 2003 Mercury Grand Marquis, and 2003 Lincoln Town Car. However, it is still accessible from the selected car via links, so may be relevant.
The Secondary Air Injection (AIR) system controls emissions during first 20-120 seconds of engine operation by forcing air downstream into exhaust manifolds to oxidize hydrocarbons and carbon monoxide created by running rich at start up.