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 -2-activates secondary air pump -12- via secondary air pump relay -1-, and air is fed to combination valve -10- (mechanical secondary air valve).
• ◆ At the same time, the system activates secondary air inlet valve -3-, which supplies vacuum to combination valve -10- and to pressure unit -7- for charge air control. In this way, the combination valve opens a passage for the secondary air system to supply air to the exhaust ports in the cylinder head.

• ◆ To avoid generating unnecessary heat, the secondary air is channelled past turbocharger -8-. This is achieved by means of the pressure unit for charge air control, which opens the charge air control valve. To perform this function, the pressure unit is designed as a two-way pneumatic unit with an additional vacuum connection on the "pull-in" side.

• Secondary air pump relay -J299
• Engine control unit -J220
• Secondary air inlet valve
  -N112
• Intake manifold

• Non-return valve
• ◆ Installation position (light side/ dark side) as shown in illustration. Arrow indicates direction of flow
• Vacuum reservoir
• Vacuum unit for charge pressure control
• Turbocharger
• Cylinder head
• Combination valve for secondary air system
• Air cleaner
• Secondary air pump motor -V101