Prob's with my Audi A6 2003 Auto 3.0 V6 (gearbox)

Not an uncommon problem for Audi owners. There is a way to override the park lock function bu this is a quick fix - you will need to diagnose the core issue with the selector being locked out. This might be of help to you -

Audi A6 C5 1997 2004 Why is My Auto Gearbox Stuck in Park

run the fault codes and check for problem TCM unit.

Auto gearbox faulty! Could be synchro mesh or gear selector?

It sounds like you may have faulty shift solenoids. (internal transmission)

You really should not drive your car in that condition.Resetting codes will not help and it's a waste of money. All indicates problem with torque converter. Service immediately!!!!

you have a transmission problem. the tcm has switched to limp mode witch means the trans will start and stay in 2nd or 3rd gear only. this requires a scan tool to properly diagnose the problem. you should get it checked out sooner than later before any further damage is caused by driving it in its limp mode. good luck.

Does it keep running till the batt is flat? It could be the aircon condenser fan running - on the left as you stand in front of the car. This is a common prob with A3s of this age.
I have a '05 3.2L Quattro V6 and suffered the same prob. The batt is in the boot of the V6 and is sealed like Fort Knox so impossible to disconnect. After about 3 days with this the fan running constantly and having to put a charger on it every night I let the batt run completely flat to try and reset the complete system - no DIS lights - no starter motor clicks - DEAD. Then I jump started it and the prob disappeared completely. Everything is working perfectly ncluding the aircon. That was 4 days ago and 'touch wood' I've had no probs since. I know this won't work for everyone but it's worth a try before forking out £300+ for a new condenser fan unit. Good luck!

Unless your shade tree mechanic is an Audi expert, go to the dealer who has all the books and diagrams that tell the tech exactly where to look. The other guy may want to replace something just to troubleshoot and the factory tech should know exactly what to replace or which plug is loose.

I have been having similar problems. The clutch is slipping as thats how you get the variable gears when in full auto, but this is where the problem comes from, some garages (auto gearbox specialists) are now able to fix it. Do not go to Audi as all they do is replace the gearbox (very expensive). There is no quick fix though! Sorry for the bad news!!

yeh got same prob.been like it for 3 months had fluid changed still doin it they found a fault.. code f115...i think..it a sensor in gearbox.£600 to get done learnt to live with problem for time bein.always seems to drive ok.and after i drive abot 20 miles all light seem to be ok.found that if i go 1 click on ignition pull down to n an start car all is ok except revers wich is ok after a short run.then do the same thing next time....but as soon as you put it in to p it al flashes again...and also when switchin off put it in to n..turn of ignition put to p and take out key...hope this helps for time bein