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Secondary air system - overview > < Checking exhaust system for leaks

A4 Mk2

Secondary air system
Secondary air system
t  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.
t  Because of the over-enrichment of the mixture in the cold start phase, the proportion of unburned hydrocarbons in the exhaust gas is higher. The secondary air system improves the afterburning (oxidation) process in the catalytic converter, and thus 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.
   
Operation
t  In the cold running phase, the engine control unit -6- actuates the secondary air pump -1- via the secondary air system relay -5-. Air is routed to the combination valve for the secondary air system -3-.
t  At the same time, the secondary air inlet valve -8- is actuated, thus allowing vacuum to reach the combination valve for the secondary air system -3-. In this way, the combination valve for the secondary air system permits passage of secondary air to the exhaust ports in the cylinder head.

   

Secondary air system - overview > < Checking exhaust system for leaks