Audi Workshop Service and Repair Manuals

The secondary air system is designed to enable the catalytic converter to heat up and reach its operating temperature more quickly after a cold start.

Principle of operation

Due to the extra mixture enrichment during the cold-start phase, an increased amount of unburnt hydrocarbons is carried in the exhaust gas. The secondary air system improves the afterburning (oxidation) process in the catalytic converter, and in this way reduces toxic emissions. The heat generated by oxidisation accelerates the "light off" of the catalytic converter and significantly improves exhaust gas quality during warm-up.

Function

• ◆ After a cold start, engine control unit -6-activates secondary air pump -1- via secondary air pump relay -5-, and air is fed to combination valve for secondary air system -3-.
• ◆ At the same time, the system activates secondary air inlet valve -8-, which supplies vacuum to combination valve -3-. The combination valve opens a passage for the secondary air system to supply air to the exhaust ports in the cylinder head -9-.

• Secondary air pump motor -V101
• Air cleaner
• Combination valve for secondary air system
• Non-return valve
• ◆ Installation position (light side/ dark side or arrow marking) as shown in illustration. Arrow indicates direction of flow
• Secondary air pump relay -J299
• Engine control unit -J220
• Vacuum reservoir
• ◆ Fitting location: in front left wheel housing behind wheel housing liner
• Secondary air inlet valve
  -N112
• Cylinder head