A4 Cabriolet Mk2
| Principle and function |
| Principle |
| Because of the over-enrichment of the mixture in the cold start phase, the proportion of unburned hydrocarbons in the exhaust gas is higher. The injection of secondary air improves the post-oxidation in the catalytic converter and thus reduces pollutant emissions. The heat generated by oxidisation accelerates the “light off” of the catalytic converter and significantly improves exhaust gas quality during warm-up. |
| Operation |
| t | In the cold running phase, the engine control unit -4- actuates the secondary air pump -2- via the secondary air pump relay -3-. Air will then reach the combination valves for secondary air system -5- and -9-. |
| t | At the same time, the secondary air inlet valve -6- is actuated, thus allowing vacuum to reach the combination valves for secondary air system -5- and -9-. In this way, the combination valve opens a passage for the secondary air system to supply air to the exhaust ports in the cylinder head. |
