PRNDS flashing - cannot connect to transmission with VCDS

**A6avantowner** · 02-09-2021,01:44 PM

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

**Crasher** · 02-09-2021,05:10 PM

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

**A6avantowner** · 02-09-2021,07:02 PM

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

**A6avantowner** · 19-09-2021,05:14 PM

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.

**Crasher** · 19-09-2021,07:02 PM

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.

**A6avantowner** · 19-09-2021,08:19 PM

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?

**A6avantowner** · 20-09-2021,08:27 PM

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........

**Crasher** · 21-09-2021,07:19 PM

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.

**A6avantowner** · 22-09-2021,11:04 AM

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