Secondary air system, overview: Function

• After a cold start, engine control unit -3-activates secondary air pump -1- via secondary air pump relay -2-, and air is fed to combination valves for secondary air system -4- and -8-.
• At the same time, the system activates secondary air inlet valve -5-, which supplies vacuum to combination valves -4- and -8-. The relevant combination valve opens a passage for the secondary air system to supply air to exhaust ports in cylinder head.

Fig 1: Overview Of Secondary Air System

Courtesy of AUDI OF AMERICA, INC.