You have just triggerd a thought. Whose lead are you using for diagnostics? VagCom (VCDS) or the full Audi lead?

If it's a VagCom lead it might be out of calibration as I had a similar issue with an ECU. My VagCom lead would not read the ECU but a mates would. I e-mailed Rosstech, they had me do a diagnostic with the debug facility set at 8. I emailed them a couple of files this generated and the e-mailed me back a calibration file that reset my lead and hey presyto I could read my ECU again!!! :)

If it's a vagCom lead (genuin RossTech) then it may just need calibrating.

What do you mean with main ECU? ECU stands for engine control module. You say You can connect to the engine and gearbox ( TCU- transmission control unit). What is the fault codes and what are You using to get the fault codes?

I'm not sure what lead was used but I'm almost certain it'll be a cheap one! The first garage gave me the errors printout but the garage its with now seem really knowledgable - they tend to do mercs/Bm's/audis ; they had a fat v12 merc in bits so gave me some confidence. They do a lot of remapping so they use the leads quite often - I'm sure they'd know if they're lead was dodgy. They probably won't get to look at it til friday so I'll keep you updated .
I've also found a place called ecu doctor that can test/repair the ecu for about £150 - no fix / no fee...... Sounds promising, if indeed it does turn out to be the ecu. I guess its quite hard to diagnose without putting a working ecu in although I presume you can check the power input line to the ecu is correct......
Really having doubts about S8 ownership at the moment, got no spare cash right now and can jst about afford to run it nevermind big repair bills....oh well

I've used the ECU doctor when my Mitsi Pajero (V6 Petrol) ECU went AWOL, had it turned around in about 3 days (by post) He's happy to talk about solutions on the phone
Did a splendid job on my Mitsi ECU, it came back much more economical, more power & better acceleration than it had ever been in my previous 8 years of ownership..... came to £180.00 was well pleased.

Hope this helps you daz

My garage has confirmed the ecu is at fault - was full of water apparently and damaged beyond repair.....
They quoted £870 all in for a new one, might just do that cos its hassle being without a car if I tried ecu doctor, especially over xmas. I am worried about possible issues with the immobiliser and keys etc as these all need go be sinked up don't they??
I understand the drain lines can be the cause, sure I've seen a fix somewhere but buggered if I can find it now - does anyone know of a link ??
Would't want it happening again......

Hi had that problem myself with the drain plugs

Try thishttp://audi-diy.blogspot.com/2007/11...or-drains.html

I just looked at Elsawin and ECU adaption procedure is the same as for prefacelift You do not need logins or anything for it. Fairly simple to do. keys are coded to immobiliser so You will not need to recode keys only need to do adaption for immo to accept new ecu.

£870!!!!

If you have the ECU part number, A8Parts may be able to help. If not with a part number I may be able to get one cheaper.

cheers conan, I've had the new one fitted cos I needed it sorted for xmas and all is well again......except the bloody radio is asking for a code now which I havn't got.
The stealers want £15 quid to tell me, does anyone know now I can get it for free ??

Glad it's sorted Daz, might be worth looking into a warranty for the future if the costs are a concern. I would only go to Shark Performance for immobiliser,ECU & radio code retrieval depending on how far he is. I think £15 ain't a bad price mind you...
Also have they sealed up or stopped the issue that was letting the water into the ECU in the first place and if so where did it develop? It might be worth others checking theirs to prevent it happening in the future. +++