Just asked my dealer the same question for my 2001. He said 100K or 10 Years.
The EPA mileage estimate for the 2003 Audi A4 is 20 mpg in the city, 29 mpg on the highway.
The EPA mileage estimate for the 2003 Audi S6 is 13 mpg in the city, 19 mpg on the highway.
The EPA mileage estimate for the 2003 Audi S8 is 14 mpg in the city, 20 mpg on the highway.
The EPA mileage estimate for the 2003 Audi A6 is 18 mpg in the city, 25 mpg on the highway.
The EPA mileage estimate for the 2003 Audi TT is 18 mpg in the city, 27 mpg on the highway.
The EPA mileage estimate for the 2003 Audi A8 is 15 mpg in the city, 23 mpg on the highway.
Yes.
Audi recomends changing timing belt and water pump at 110k miles.
Very
It must be changed every 90,000 miles. Warning: This is an interference engine and as such if the belt breaks serious engine damage will occur.Update: Audi now recommends every 75,000 miles.
...timing of audi tdi
audidiy.com