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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

1 2 ... 20 21 22 23 24 25 26 27 28 29 30 ... 119 120

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BMW M5 Wartungshandbuch Seite 25