Principle and function

WARNING: This page is about a different car, the 2006 Audi A4, 2005 Audi A4, 2004 Audi A4, 2003 Audi A4, and 2002 Audi A4. 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 startup time of the catalytic converter considerably, as well as significantly improves emissions quality during the cold-running phase.

Function

During cold start (with coolant temperatures +15 to +35 °C), the Secondary Air Injection (AIR) system blows air behind the exhaust valve for approx. 65 seconds. This produces an oxygen rich exhaust gas, causes the after burning and reduces the heating-up phase of the catalytic converter.
In addition, the Secondary Air Injection (AIR) system is switched on with a delay of approx. 20 seconds during idle for 5 seconds after every engine start up to max. 80°C coolant temperature and is checked via On Board Diagnostic (OBD).