Audi has determined that, under certain driving conditions, carbon buildup can occur in the engine cylinder head secondary air ports. Due to the presence of specific fault codes caused by this carbon buildup, the Malfunction Indicator Lamp (MIL) on the instrument cluster may illuminate. The MIL is part of your on-board diagnostic system. Please refer to your owner's manual for additional information about the MIL. In some locales, an illuminated Malfunction Indicator Lamp could cause your vehicle to fail an IM emissions inspection, and your vehicle registration application could be denied. Please be aware that other conditions (unrelated to the issue described in this letter) may cause the MIL in your vehicle to illuminate. Customers should be prepared to cover all diagnosis and repair costs for these other, unrelated conditions.