Principle and function

WARNING: This page does not describe the selected car, but rather 6 other vehicles, including the 2009 Audi S4, 2008 Audi S4, 2007 Audi S4, 2006 Audi S4, and 2005 Audi S4. However, it is still accessible from the selected car via links, so may be relevant.

Principle

Due to the rich mixture during the cold start phase, the exhaust emissions contain an increased level of unburned hydrocarbons. The Secondary Air Injection (AIR) system improves the secondary oxidation within the catalytic converter, thereby reducing harmful emissions. The heat released by secondary oxidation shortens the start-up time of the catalytic converter considerably, as well as significantly improves emissions quality during the cold-running phase.

Function

Fig 1: Secondary Air Injection (Air), Component Overview

Courtesy of VOLKSWAGEN UNITED STATES, INC.

In the cold start phase, the ECM - 3 - activates secondary air pump - 1 - via relay for secondary air pump - 2 -. Air reaches combination valves for Secondary Air Injection (AIR) - 4 - and - 8 -.
The Secondary Air Injection (AIR) valve - 5 - is activated in parallel, which allows the vacuum to reach the combination valves for Secondary Air Injection (AIR) - 4 - and - 8 -. The appropriate combination valve for Secondary Air Injection (AIR) thereby opens the path for secondary air to the exhaust channels of the cylinder head.