Technical data

15
8
Secondary air system
After the engine has been started, the electric
secondary air pump mixes fresh air with the
exhaust gas to bring about oxidation of the
uncombusted hydrocarbons in the exhaust
gas. As a result, the HC component in the
exhaust gas is reduced and the light-off
temperature of the near-engine main catalytic
converters is reached at a faster rate. To
conform to the stringent exhaust emission
regulations in the USA, it is necessary to
control the secondary air. This is achieved by
an idle speed actuator in the secondary air line
on the US version of the S85.
The secondary air is injected into the exhaust
ports via vacuum-controlled diaphragm valves
on the cylinder heads.
The vacuum necessary for activation of the
secondary air valves is taken from the cylinder
head 6 - 10 and switched by an electric
changeover valve. A check valve prevents the
return into the cylinder head.
The vacuum lines from the electric
changeover valve to the secondary air valves
are routed in the wiring harness duct.
19 - Secondary air system
Index Explanation
1 Diaphragm valve
2 Secondary air actuator (US version
only)
3 Secondary air pump