heating AUDI A4 1999 B5 / 1.G APB Engine Secondary Air System Workshop Manual

26-31


Secondary air system The secondary air system results in quicker heating
and therefore earlier operating readiness of the
catalytic converter following cold start.
Principle
Due to over-enrichment of the mixture during the
cold start phase, there is an increased amount of
un-combusted carbon monoxide in the exhaust.
Secondary Air Injection (AIR) improves secondary
oxidation in the catalytic converter and therefore
reduces emissions. The heat produced by
secondary oxidation greatly reduces start-up time
for the catalytic converter, therefore improving
exhaust quality during the cold start phase
significantly.
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