PRNDS flashing - cannot connect to transmission with VCDS

I would really appreciate some advice with my A6 C5 2002 2.5 TDI.

Just had the TCU repaired and I re-installed it back into gearbox, following the fault logged by VCDS (17090 - Transmission Range Sensor (F125): Implausible Signal P0706 - 000 - - - Intermittent)

I did a short test drive before the car juddered and then PRNDS flashing on dashboard.

I 'limped' home and got the car back on my drive.

I now cannot connect to the TCU to troubleshoot:
Address 02: Auto Trans- Labels: 059-907-401-AKE.LBL Controller:
Note: Excessive Comm Errors

I did only manage to connect to the TCU a few times before the fault.

The TCU repair specialist is happy to test it for free, but I would rather connect to it first and diagnose (if possible).

Ross-Tech support have advised me to check wiring, but not sure how do do this.
I'm using a registered VCDS Lite with a Gendan USB KKL VAG diag cable. Connects OK to all other modules on car.

Any ideas and advice very welcome.

Thanks

I had one of those CVT units "repaired" once, that was the last time I tried that. Who did it, ECU Testing?

Hi Crasher
Thanks for the reply.
It wasn't ECU testing, I nearly tried them.
It was Control Units - they were very helpful and said they would test it for free. The unit was a previously repaired one which I discovered when I removed it from the gearbox. I had a recon box back in 2014 and it's run well until very recently. I'm hoping it's not the TCU but it probably is.
Regards

Update.
Managed to connect to TCU with VCDS following advice from Ross-Tech (VCDS software setting).
Original fault (F125) returned.
ControlUnits have now repaired and I'm installing tomorrow. They confirmed that the unit was still faulty.

Which is why we will no longer fit used or repaired electronics any more (and I emphasise any more) as the amount of stress these parts have caused us is intolerable… imagine if you were your customer.

Yes I get that, but my car is 2002 and it's not viable to get a garage to repair. I paid over £700 plus labour for a new TCU back in 2011. And this TCU was a previously repaired unit (Bristol Transmissions refurbished my gearbox in 2014) and it lasted almost seven years. So I either scrap the car or attempt to get it running at a viable cost. I've got some time on my hands at the moment so it works for me (I hope!).
Just to add, I thought Bristol Transmissions refurbished my gearbox, but I discovered it's not my original but from an A4 with a repaired TCU. It would have been good to know this as I paid £2,400 but as it lasted seven years I can't really complain. I wonder what happened to my TCU that would have been three years old at the time?

Update
Installed the repaired (twice at least) TCU and put everything back together and filled with CVT fluid.
PRNDS still flashing!
VCDS showing original error (f125 etc...) - cleared codes but keeps coming back.
This is becoming a very long task.
Will have another look tomorrow........

You have only three choices, keep throwing repaired/used units at it, fix correctly using a genuine part. The F125 switch error can only originate inside the box controller so all other fixes are ******* in the wind.

How much does a new unit cost, and if I get one I don't think that VCDS Lite (registered version) can encode the new unit?

I've just been advised to clean the selector shaft and check the spring. It looked ok when I installed the TCM but maybe it needs a closer look. Would a problem with the selector shaft throw up the F125 fault??

Regards

The most common thing we would see was metal particles stuck to the magnets but that’s obvious. I need the REG to identify the correct part.