Only in 16V engines
The task of secondary air charging is to cause additional oxidation of the exhaust gases during the warm-up phase of the engine and to reduce the starting time of the catalytic converter.
The blown air serves to burn off unburned components still contained in the exhaust gases. To do this, the electrically driven secondary air pump (mounted on the front left next to the battery) presses - depending on the operating mode of the engine - the purified air into its exhaust channels. The air filter is located behind the radiator grille. There is no filter change interval.
Due to this, on the way to the catalytic converter, additional oxidation of the exhaust gases is carried out, as a result of which the emissions of hydrocarbons and carbon monoxide are reduced; the flue gas temperature rises. Due to this, the catalytic converter and the lambda probe reach operating temperature faster; lambda control works earlier.
The secondary air is activated after the engine is started. It does not have a separate control unit, it is started by the ignition/injection control unit. The secondary air boost is switched off with the activation of the lambda control. The air flow is controlled by a shut-off valve, which is opened and closed by the changeover valve by means of reduced intake manifold pressure. A non-return valve next to the engine prevents pressure surges in the piping system from reaching the secondary air pump. The function of turning the secondary air pump on and off is performed by the ignition/injection control unit. Due to the current consumption of the pump, an intermediate relay is installed, which is located in the box with the relay (in the engine compartment next to the battery).
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