My sons 2.Tdi Quattro triptonic shows aconstant 350 per tank 30mpg but this is mainly slow mway commutes of about 10miles .My manual version same car will give 450 or 35 mpg mainly urban use.Both have tuning boxes but it seems its more effective in mine.Both are much better in open road longer journeys so it depends on how you use them
Mine is a 2.5TDI wauttro manual, but the warning light comes on when I am 50litres into a tank (i.e. around 15litres remaining): given that I've usually done anything from 300 to 400 miles by this stage, I reckon I could get 450-500miles on a tank if I was running it to empty (i.e. over 100 miles with the "0 miles remaining" light on).... I've got >400 miles a few times and usually put <60 litres into the tank afterwards.
Once general be-puzzlement: you state that you have a:
I assume you mean a 2.5TDI quattro AUTO (tiptronic, but regular auto)... as I'm pretty sure that the the multitronic (CVT) gearbox has never been fitted to any Audi quattro system, certainly not in an A4 B6.
Currently getting around 500 to a tank in my 2.5 quattro 180 manual, Tbh i really dont notice a difference in fuel consumption over my last 1.9. Probably because i dont have to drive it as hard to reach the same given speed.
To answer the original thread: for my manual quattro V6 TDI under normal, moderately enthusiastic driving, I'll be around 375miles miles before the light comes on... but I think my light does come on early (50 litres out of 65 litres consumed).... the most I've seen before a light was a sniff under 450 miles before the light came on, but that was a pre-warmed motorway cruise and I WAS driving Miss Daisy.