32
Engine - Motronic Subsystems
Secondary air system
Owing to the high mixture enrichment during
the cold-start and warm-up phase, an
increased proportion of unburnt hydrocar-
bons exists in the exhaust gas during this
time.
The catalytic converter cannot process this
high proportion of hydrocarbons because:
1. the required operating temperature of the
catalytic converter has not yet been
reached and
2. a lambda 1 mixture must exist to allow
complete conversion.
Air injection downstream of the outlet valves
causes oxygen enrichment of the exhaust
gases. As a result, the hydrocarbons and the
carbon monoxide undergo post-oxidation
(afterburning). The thermal energy released
during this process also heats up the catalytic
converter so that it reaches its operating
temperature more quickly.
The secondary air system consists of
– the secondary air pump V101
– two combination valves A + B
– the secondary air inlet valve N112
J220
N112
G108
J299
V101
G39
G70
G62
SSP217_042
Energised
Not energised
A
B
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