Emission Control Systems: Description and Operation

Secondary Air Injection







In order to achieve compliance with the worldwide emission limits, the models Cayenne S Hybrid (worldwide), Cayenne S (in EU5 markets) and Cayenne Turbo (EU5 markets) feature secondary-air injection. The secondary-air system provides faster heating of the catalytic converters and a reduction in exhaust emissions. For this purpose, air is injected into the exhaust tract behind the exhaust valves for a defined period after the engine cold start. The uncombusted hydrocarbons and carbon monoxide either contained in the exhaust gas or deposited in the catalytic converter then react with the oxygen in the air. The heat that is released means that the operating temperature of the catalytic converter is reached more quickly.

Secondary-air Injection Valves

System test for engines complying with ULEV II emission standard

Here, the test must be carried out during the warm-up phase for the catalytic converters. However, the oxygen sensors do not reach operating temperature quickly enough. An additional pressure sensor (secondary-air pressure sensor) is therefore used for diagnosis. It is used to carry out pressure-based secondary-air diagnosis. In this system, the signal is evaluated by the secondary-air pressure sensor in the engine control unit. The injected air quantity is deduced from the pressure level.