catalytic converter AUDI A4 1999 B5 / 1.G AWM Engine Secondary Air System Workshop Manual

26-41


Secondary air system Secondary air system,
function/components

The secondary air system permits faster warm-up
and thus makes the catalytic converter ready for
operation sooner after cold starting.
Principle
Due to over-enrichment of the mixture in the cold
start phase, there is an increased amount of
unburned hydrocarbons in the exhaust gas. The
injection of secondary air improves the oxidation in
the catalytic converter and thus reduces emissions.
The heat produced by secondary oxidation reduces
start-up time for the catalytic converter therefore
improving the emission quality in the cold-running
phase.
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