Hi guys

I'm looking at buying a A6 (C6 2.0 TDI diesel S Line). I've found one that I really like the look of, which is sensible money but has a fault:

On the dash the trip computer mileage does not rise as you drive, but the normal mileage does.

Additionally, the fuel always shows as empty.

I assume these are most likely linked??

Why would mileage rise, but not the trip computer???

I'd like to know what I'm most likely facing before I take the plunge and buy it.

Any help very welcome!