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Audi TSB #A011257 2028344-
2011 Audi S6
Affected Component: ENGINE AND ENGINE COOLING:EXHAUST SYSTEM:EMISSION CONTROL:CATALYTIC CONVERTOR
- Supersedes Technical Service Bulletin Group 01 number 12-51 dated July 18, 2012. Noises/inconsistent engine operation after cold start during the catalyst heating phase. The customer may interpret this engine roughness as misfiring. To comply with the legal requirements on exhaust gas emissions according to the LEV-1 and LEV-2 standards, a high exhaust gas quality must be ensured. The necessary catalyst only operates at a temperature over 300°C (572°F). To achieve this, the catalyst is heated up. The catalyst heating phase is achieved by a late ignition angles and by introducing additional fresh air to the exhaust valves (secondary air system). Late ignition angles make sure that the exhaust gas from the cylinders has a higher temperature. This exhaust gas includes fuel that is un-burnt, and was deliberately injected into great quantities. The secondary air system adds fresh air to the exhaust gas as it leaves the cylinder and the extra fuel is burnt. As a result, the temperature of the exhaust gas and of the catalyst increases quickly. The afterburning in the exhaust manifold before catalyst changes the sound characteristic of the engine. This heating-up of the catalyst, including afterburning, is normal and has no effect on the service life of the engine. During this catalyst heating phase the engine has increased idle speed, may have increased vibrations, and a different sound characteristic. Depending on conditions the time of the catalyst heating phase varies.
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