audi a6 autobox

[golf tdi 02]

hi to everyone if poss need a little point in the right way please just been offered a audi a6 r reg 1.8 turbo with auto box the problem is that it drives through the box in tiptronic mode but not in drive mode is this something silly like a sensor or is the box .
has anyone had similer probs and what was the outcome
many thanks rich...:1zhelp: