A4 B6 CVT Speedomter Not Working, No Errors or Warnings

[FilipStojkovic]

Hello people,

Problem:
I have serious problem with my Audi A4 B6 2.0 Petrol with CVT trans.
My car was working normal, even CVT was all right, no PRND warning lights, no rough acceleration, jerking etc.
Suddenly my speedometer died. Id measures max to 50-60 km/h. After that trans starts to jerk, engine struggles with it, revs go up and down, really not drivable. Below 50km/h it works normal.
On the highway i switched to multitronic mode, and manually shifted to (virtual, since its CVT) 6th gear. That way i can drive 120km/h+ (measured with GPS), but speedo still shows 60km/h.
As i said, i can manually shift even in urban driving conditions and it is (almost) drivable, but still speedo not working, and driving in D is not good.

What i tried:
What I tried so far is that i lifted the car up, drained CVT fluid, removed TCU, opened it to check for some burns or cold solders on computer board, and everything is fine. I checked sensors for input and output shafts, and they both work as they should.
I properly closed TCU, put it back, filled CVT fluid back into trans. Car works exactly as it did before i did this.
I checked all error codes in both engine, abs and transmission, before and after lifting the car. There are no errors in any of them.

As you can see i totally don't know what to do. My car is in garage for few weeks now, i dont drive to prevent any further damage.
I would appreciate any help from you people!

[diagnosticator]

Perform the driving adaptation procedure. That should allow the TCU to relearn the correct parameters for proper operation. The speedometer is driven by the speed signal sent from the ABS module possibly the signal from the ABS module is faulty, or the ABS module is defective. Or, the instrument cluster is faulty.

[FilipStojkovic]

diagnosticator, thank you for your reply! I will perform adaptation today. I attempted to disable ABS completely by disconnecting cables, to see what will happen. ABS light came on on cluster (as expected), but car was driving exactly same as with ABS on. That leads me to believe that TCU currently is not taking any speed related info from ABS module (maybe car entered safe mode somehow because ABS is defective). I was reading that CVT TCU relies on both ABS info and input and output shaft sensors in transmission itself to compute current vehicle speed, is this right?

[diagnosticator]

diagnosticator, thank you for your reply! I will perform adaptation today. I attempted to disable ABS completely by disconnecting cables, to see what will happen. ABS light came on on cluster (as expected), but car was driving exactly same as with ABS on. That leads me to believe that TCU currently is not taking any speed related info from ABS module (maybe car entered safe mode somehow because ABS is defective). I was reading that CVT TCU relies on both ABS info and input and output shaft sensors in transmission itself to compute current vehicle speed, is this right?

Vehicle speed is determined from just the wheel speed sensors sent by the ABS module as a speed signal to the speedometer. The transmission shaft speed sensors are used by the TCU to determine transmission engagement and shifting strategy.

BTW, the CVT transmission fluid is specified to be changed every 40K miles. Did you use fresh new CVT trans fluid when you drained and refilled the trans?

[FilipStojkovic]

I will perform some in depth check on my ABS sensors, wiring and module, when i get home, thank you :)
As for CVT fluid, i replaced it with fresh fluid when i bought the car, about 2k miles ago, and car performed much better. So i decided to put back that same fluid when i refilled it yesterday.

[FilipStojkovic]

Hello, I am happy to say that i fixed my problem! After about month and a half of driving the car i carefully observed when the problem occurs. I read 01J (my trans code) documentation, and concluded that the problem was SLIPPING SENDER WHEEL for g195 and g196 sensors. Opened trans, sender wheel (small rubber ring with 32 magnets molded inside) was pretty loose and I was able to remove it just by touching it. I was pretty sure that was the cause of my problems. Cleaned it, put the silicone on it, put back, wait few days, put everything back, fill back with fluid, and car works great now! :))