Replacement transmission is junk, TCM bad? Or I might be crazy.....

[Jeros]

A little background,

Have been working on cars for many years, and have replaced my share of transmissions. I have a 2009 A4 wagon with a 2.0t and 6 speed trip automatic. The insides started making some pretty substantial bearing humming noises, so I bought a used one and threw it in. I replace the filter, fill it up with fluid, start the car, and nothing. No output in any gear. The torque converter is pumping fluid, it has enough fluid, but nothing. The dash display says something along the lines of "transmission fault, limited functionality, you may still drive"

Is there any recoding required to get the vehicle to recognize the new transmission? The transmission acts like it is just not getting any commands. The old transmission shifted perfect, would taking the TCM and valve body out of it and installing it in the new transmission potentially solve the problem.

Oh, and because I am a glutton for punishment, I put my old transmission back in, and aside from the awful noise, it drove and shifted fine.

Any help would be appreciated!

[treginginco]

There are going to be coding items that need to be done. The engine and transmission need to
Speak with each other. Control units need to be compatible.

I'm basing this on an old Touareg that had a transmission swapped and I was told the mechanical
Part was easy --- the software flashing between the engine and trans was absolutely necessary

[Jeros]

I'm thinking along the same lines. I called the dealership and asked a tech if there was any coding procedure required to get the transmission to communicate. They said they weren't aware of any and I should just be able to install a used transmission and go. Im going to call around a bit more, and if Im feeling brave, am also going to through that valve body/TCU from the original transmission and see what happens.

What about this procedure?

http://www.ross-tech.com/vag-com/cars/autotrans.html


I cant tell if its meant for every new install.

[Jeros]

Car is moving again! Little update for anybody that comes across the same problem. Still not 100% if a coding of the TCU is required after putting in a new transmission.

I called around to a few dealerships and couldnt get a straight answer. Some said that a coding wasnt required, and others said they think they are required and that their guys could do them. I also called a local key coding and computer programming company. They said they couldn't find any documentation on whether it required coding or not. If anybody comes across a clear answer, Id be curious to know. Since I didnt want to waste money with something that wasnt a sure thing, the only option left seemed the most sketchy. I took the whole TCU/valve body/harness out of the old transmission and put it in the new(used) one.

The TCU is located above the valve body inside the transmission. It comes out in one whole assembly. You have to drop the pan to get inside there. It can be a messy job. Even after the fluid is drain, ATF is still dripping everywhere as youre trying to work. you have to be very careful not to let any foreign contaminants get on the mounting surfaces of the valve body or in any of the open ports of the valve body. Alighning the shift mechanism with the valve body is kind of a pain in the ass. I screwed it up the first time, and the car wouldnt start because it thought it was in gear. After getting everything straightened out, reinstalling the filter, filling it up, and buttoning everything down, the car started fine and drove around. I still have to test drive it on the highway.

So yeah, using my original TCU/valve body worked. The ECU was able to communicate with the transmission again.

[Jeros]

Final update for anybody interested. The car is running and shifting fine. I've done some more reading on the issue and it seems that if you get a TCU for the same car, with the same instrument cluster and drivetrain, there shouldnt be an issue. If the transmission, and therefor, the TCU came from a different setup or model, it will likely have to be reprogrammed. The six speed behind the 2.0t came in many different models, and my transmission came from something different than what I had. This is something that recyclers should know, because obviously it is a compatibility issue. An audi dealership should be able to do the programming. It's no different that any software update that they do all the time. The service managers likely aren't aware of this issue though because it's just so rare. Goodluck anybody else.

[NLPed68]

This is good info to know. Thanks for doing this and posting your findings/conclusions!