Ok, here's Audi UK's reply ;
Thank you for your recent email regarding the cambelt on your Audi A6.
I can confirm that The cambelt (also known as the timing belt or toothed belt) is normally located at the front of the engine. The timing belt connects the crankshaft and the camshaft, thus synchronizing engine timing. The camshaft on the cylinder head ensures the regular opening and closing of the valves, so it is necessary for it to turn at exactly half the rate of the crankshaft.
The cambelt also:
• Drives the injection pump
• Drives the water pump
Full functionality must be guaranteed in all driving situations throughout its entire service life.
Audi UK recommends a cambelt change interval of five years or 140,000 miles, whichever comes first, for the above vehicle. This is to ensure optimum safety and performance.
The cambelt is one of the hardest-working parts in the engine. Any component working this hard will eventually show signs of fatigue. A worn or damaged belt could become slack or even snap, often causing severe engine damage which is very expensive to repair.
The mileage replacement recommended by Audi AG is not always relevant to conditions experienced by Audi customers in the UK.
Stop-start journeys on congested roads may cause additional wear on parts compared to the optimum conditions experienced in some parts of Europe.
The revised recommendation introduces consistency between retail and fleet and will protect customers with very low-mileage cars from cambelt failure. Cambelts are rubber-based components that can deteriorate over time and it could be many years before these customers reach the recommended mileage interval changes.
Thank you for sharing your concerns with us, allowing me the opportunity to reply. I hope that I have been able to explain the background to the cambelt in your Audi A6 Avant and give you some transparency in this regard. If you would like to discuss the above or have any other queries, please contact me on the details shown below.