DL501 TCU comminication lost (u0101)

[Robmkr]

Hello everyone.

I have A7 2011 (3.0 TFSI) WITH 05B (DL501) Transmission..

My problem is when starting the car after 8-10 hours stanby I dont have transmission at all. Error code is u0101 lost communication with TCU.

And I cannot see PRLND in my dashboard at all.

After warming car about 3-5 minutes, its coming back, showing gearbox mulfunction error on dashboard, and after restarting the car everything is working fine. Heppens only when car parked outside and its cold ( I'm in Dubai, so cold I mean around 15-20 C)

Never happened while driving, never happened on hot period of summer.

I checked the connecter on TCU which is from outer side of mechatronic, changed the battery with no luck.

I'm wondering if someone faced this issue before and any help would be appreciated.

Apart from that I have a clunk when putting on R from P every time. While driving no issues at all, no slippage, no kicks. It works smooth, only problem is R and the lost communication error.

P.S. when that happened I have the same message in almost 10 different modules (engine, instrument cluster, tpms, ...)

Never happens when car is warm. I mean starting after 30 min stanby lets say.

Its happening more and more with the cool season ( again cool is around +15 degree of C)

8 months ago I have changeed the clutches, rebuilt the mech unit and changed the TCU.

I was thinking about faulty TCU, but the question is why its never happening while driving.

Thank you.

[Robmkr]

UPDATE: Changed the battery, same.

UPDATE 2: Tried to disconnect battery overnight, same result :D

It's basically in limp mode every morning now. After warming for 5 minutes, transmission is coming back and working normal, like that issue never ever happened.

[last_mile]

Hey

Did you diagnose the issue?

I faced a similar issue for my A6 C7. Same error code. TCM was randomly loosing communication. Eventually had to replace the TCM. Expensive affair.

[Robmkr]

Thanks for the reply.

The funniest part is that car is working fine after 5-10 minutes when its become warmer.

Never happened while car is warm, so likely issue is inside the transmission.

Took it to sorkshop who fixes the box 9 momths ago.

They will pull out transmission, lets see what sursprises I will receive.

Seems its either TCM itself or wiring harness going to the TCM.

[rpwizard]

same issue was a cable in the wiring harness on the tkm connector re-wired and work all :)

[Robmkr]

Inside the mech unit? If you mean the round connector which is connected from outside of transmission, I've checked that, not even single sign of problem. If you mean something inside the mech unit, if you have pictures, could you please share?