Converter lockup on tiptronic gearbox

[sjordet]

Hi!

I have a question regarding converter lockup on a tiptronic gearbox.

Symptoms:
- For the first 30-ish minutes, everything is as expected. Always.
- After 30-ish minutes, when I having a steady pace at 70-80-90 km/h, the converter often does not lock.
- If it's a hill, or I put the pedal down a good bit - the converter locks.

I have had similar symptoms since I bought the car over six years ago, but only when temperature was around 0 degrees. Started 5-10 minutes after start, and just lasted a couple of minutes. But only happened a few times during each spring. Now it's much more often (but not always). Doesn't affect drivability much, since it locks when I'm a bit heavy on the pedal, but it's a bit annoying when I cruising on flat roads.

Spoke to gearbox-specialists, they said it was highly unlikely that my converter was bust (yet). I will eventually get a real diagnosis by them, but as I won't have time to go to a specialist for some weeks yet, I wanted to hear your opinion.

There are no fault codes (never been any on the gearbox), and the gearing itself is smooth, I reckon. Never had any problems (with gearbox...), except this lockup-issue. I have been looking at some measuring blocks, and in group 7 it says "TC Open" under "Torque Converter Clutch" when my symptoms occur. But I don't know if it's just stating the obvious fact that it's not locked, or if it's saying that it's not even trying to lock.

Does anyone know this? Can the "Torque Converter Clutch" saying "TC Open" mean that it should have been locked, but it isn't? Or does it simply mean "not trying to lock"?

Assuming the converter itself is good, what could cause it not to lock? The specialists said that it won't lock if gearbox oil temperature is sub-zero, but VCDS said fluid temperature for 68 degrees when this happened, so I don't think the sensor is bust...

Any ideas would be appreciated

[ametlib]

Sjordet, glad to see you're back with another interesting issue !!
As usual you'll have to get to the bottom of this just by yourself , but in the meantime I,ll be more than happy to misslead you .
Ok, first thing first, when the TCU state " TC open" it's not trying to lock. If the TCU try to lock , and that don't happen, it will throw a code based on the rpm differences between the engine and the incoming shaft
in the transmission, but it will still state "locked".
Based upon what you wrote, I'm pretty sure your converter is ok. AFAIK the converter should always be locked up if the ATF is over 17 degrees C and the cars speed is above 45 km/h. There are two exeptions, the first
is when the ATF is abowe 120 C, then it will lock up at lower speed. The other is at high speed, and you really gives the throttle. If the cars speed isn't picking up fast enough, it will open the TC clutch.
Have no idea what is making the TC cluch to open, could it possibly be wrong info about the actual engine torque from the ECU ?

[sjordet]

Hahaha, thank you ametlib! It seems there are not that many tiptronic in the UK - don't know why. So perhaps you are my best hope anyways

Yeah... I have some curious problems, for sure. But my last problem are really, really very much solved. Unless it's somehow connected... Heh.

I'm happy to hear that when it says TC Open, it really should be open. Then it seems that there is nothing wrong with the converter and whatever mechanical part doing the locking. At least it seems like that.

So then the question is why isn't the gearbox told to close the TC clutch? From my logging, there doesn't seem to be any discrepancy on the ATF temperature.

That makes your suggestion about wrong info about actual engine torque from ECU being wrong... How is it measuring that? To be sure I have tried both my "new" and my "old" engine ECU, and that doesn't make any difference. So either the problems is the gearbox ECU (but come on!), or there is some sensor somewhere...

[ametlib]

Hahaha, thank you ametlib! It seems there are not that many tiptronic in the UK - don't know why. So perhaps you are my best hope anyways

Yeah... I have some curious problems, for sure. But my last problem are really, really very much solved. Unless it's somehow connected... Heh.

I'm happy to hear that when it says TC Open, it really should be open. Then it seems that there is nothing wrong with the converter and whatever mechanical part doing the locking. At least it seems like that.

So then the question is why isn't the gearbox told to close the TC clutch? From my logging, there doesn't seem to be any discrepancy on the ATF temperature.

That makes your suggestion about wrong info about actual engine torque from ECU being wrong... How is it measuring that? To be sure I have tried both my "new" and my "old" engine ECU, and that doesn't make any difference. So either the problems is the gearbox ECU (but come on!), or there is some sensor somewhere...

He,he, or wireing ? Can't really see any sensor doeing this, exept from the atf temp sensor ( wich, by the way, is only a NTC resistor in the internal transmission wireing) I think you can read the actual engine torque in
trans. measuring blocks.The TCU is placed under the carpet in front of the passanger seat and have a nasty habit of getting wet. ( Makes it go really grumphy and light up a lot of lights in the dash, but unlock the TC. ? Really dont know)
If your car have ESP or/and ABS, check in measuring blocks that all 4 wheel sensors are reading right.

[sjordet]

After some googling I have found others with similar symptoms, only happens after a certain amount of time and/or is temperature related.

One guy with a Passat in the US even replaced the TC and it didn't help! Common to those I have seen is that noone have found a solution. All of these were petrol engines - one were even a Porsche. Interesting. Probably something I will not find the cure for :/

Feel that it's unlikely to be wiring, since it happens only after about 30 minutes... Will look at the actual engine torque, and see if it differs from 10 minutes after I start, to 40 minutes...

My car doesn't have ESP, but it does have ABS. Can check those as well, but as I know the ABS-light is very happy to light up if there is the slightest problem. Replaced wheel bearing this winter, and the workshop used a lot of time getting the ABS-sensor right after that... (But my problem existed before that).

I feel a bit stupid for coming here with all kinds of impossible questions... :/

[ametlib]

Impossible question ? I rather call them interesting, nothing stupid about that !
Regarding your trannyproblems, since there are no faultcodes and nothing obvious ( at least for me, BUT I,m not a tranny expert ) this is all about guessing.( but I can do that )
First your tranny, I really belive it's perfectly ok and that the N94 solenoid is only doing what it's "told" to do. Getriebesteuergerat or the TCU, I dont think it have been wet, because it usually behaves a lot worse if that happens.
But, if nothing else fix this, I would have take it out and opened it , it's also possible ( but not very likely though) that the dealers garage did a crappy update back in time.
Signals going to the TCU : ABS-controller, Brakelight switch, ECU and probably a few moore, I would have start there

[kid-jensen]

I know this doesn't help much, but my 2002 Allroad TDI did the same thing.

I didn't notice it changing with temperature, but that could just be because I'm not sufficiently observant..

It was a bit of a pain really, because the diesel engine was a noisy old lump and it used to rev pretty high, making what passengers described as "a bloody row" before the Tip eventually locked, and the revs came down.

I used to get the occasional intermittent TCU error code, but they took several weeks to come back when I cleared them.

The car drove like this for nearly 2 years and never got any worse (or better). The next owner never noticed it...

[sjordet]

This weekend was quite hot in Norway, and I had a quite long trip. And the problem was worse than usual. This is a very far fetched idea, but since it somehow seems related to temperature, can it be because my electric radioator fan is not working? Could that influence something?

I don't know when it stopped working, I just noticed late last summer, but might have been (a lot) longer. Since neither water temperature nor oil temperature seems higher than normal, I haven't bothered with it. But maybe it's affecting something else that again influences my converter lockup?

I know this is not very likely, but somehow it for sure is related to temperature. Hmm. Interesting

[ametlib]

Doesn't seem very likely that a bad electric fan makes the TC unlock, because one of the TCU maps makes the TC lock up earlier ( lower speed and also in 2nd) just in order to lower the ATF temperatur.
A bad fan is more likely to make the AirCon not working. Ther is a programming in the TCU that makes the TC unlock if the car doesn't pick up speed fast enough. This should only happen
at high speed and if you really give it throttle.

[kid-jensen]

The only action you can take without spending serious money is a transmission oil change, so if you have more than say, 60K miles it's worth a try.

Any problems the transmission has will be made worse at higher tamperatures, so probably a good idea to fix the fan. You could wire it permanently on (with the ignition) as a diosgnostic to see if that makes a difference on a hot day...