black-series

Ok, good to hear that the values back up my guess. Under these circumstances it might be wise to change them all out. They are not very expensive and worth the price for the peace of mind, at least to me. I would really like to not have to touch my transmission ever again.

alexanderfoti

I agree. best to do it all at once.

JohnLane

Mmmmm.... Diagnosis via stripper pole....

In in all seriousness.... This one smells of solenoid that hangs.

One wonders if unidentified bits are pieces of solenoid insulation....

Hmmmm....

Galling on torque converter nose.. Look closely at flex plate for cracks or.... Did we find loose torque converter fasteners upon disassembly?

black-series

No cracks, no loose fasteners

black-series

I don‘t know what to say... Transmission is back in the car, drove 1km, error is back. I can‘t believe this is happening.

Here is a small summery for those who do not want to read the whole thread:

Under light acceleration from 50km/h the car goes out of gear during auto downshift 4-3. CEL comes on, code P0730.
What I did already:

- new conductor plate
- checked TCU for oil contamination
- new shift solenoid 3-4
- complete overhaul and cleaning process of the transmission including torque converter and cooler (done by a
transmission specialist). Two slightly worn clutch packs have been changed. The whole transmission is in perfect
condition now.
- oil is completely new as well, of course.
- Adaption values have been reset after overhaul.
- transmission oil level checked several times with a dipstick, cold and warm, spot on

I would highly highly appreciate any ideas, I do not know what else to do.

maw1124

Maybe oil in the connector, or wicking it’s way up the harness to the TCU. So the TCU and harness are actually one thought, with two possible solutions. I’m pretty sure someone has looked at this already, but just in case they haven’t...

GL

maw

black-series

Yes, I mentioned it under point two: “ checked tcu for oil contamination.“ This includes the harness as well.
Thanks anyways.

maw1124

Ok... did you reflash the ECU, to rule out a communication problem between the two? I would expect the ECU to re-initialize with the battery disconnected for the transmission work. But I might take it to a dealer to make sure I had all the latest software updates. We’re down to the checklist guesses now. I read somewhere that you need a special tool to erase transmission codes (SDS).

maw

black-series

No, I did not do that yet. Strangely enough reflashing the software for the tcu did solve a similar problem for a friend of mine. I don‘t really believe in a control unit losing its software though, hard to imagine for me that reflashing might help. But for what it‘s worth, I might give it a try. Seems like an easy next step.
I did not disconnect the battery for the transmission work.

maw1124

Yeah, lots of dark logic going on between those computers nowadays. The hardware hasn’t changed much, but the software is a completely different beast. Recently I got a tune on my M3 and out of nowhere it started throwing a running rich code. The solution was not the tune, but to upgrade to the latest FACTORY software on which the tune was based. Made no sense to me, but there you have it. I’m all for independents and DIYers. But every now and then I make a dealer update all software. Just to save me some gray matter.

maw

black-series

You are absolutely right about the computers being dark logic sometimes. I am going to make an appointment for a software update next week. I don‘t have too much hope to be honest.

alexanderfoti

Sorry to hear you are having problems. I had thought we had cracked it.
I do think you are onto an issue with the control electronics now, but the solenoid was more likely. You quite possibly have a faulty EGS control module I think. Might be an idea to swap another from a known working car if you can?

black-series

This would be my second next step, I thought about that option as well. Might give the software update a try first though. I did not manage to get it done this week.
As far as I can see, these two things are my final options, there is nothing else I could think of.
I consider the cable harness and a faulty abs sensor quite unlikely as I get my error always under the exact same load condition in the same gear changing scenario. The error would occur more randomly otherwise.

alexanderfoti

My impression of the failure mode is that the EGS controller is controlling the solenoid during the failure. The first bet would be that the solenoid is faulty, which has been ruled out. The second option could be that the mosfet or driver in the EGS module, for that solenoid is faulty. Of course, the wiring between the two could be faulty as well but its a long shot!

I wouldnt think its an ABS sensor fault. An ECU swap would rule out the ECU easily though.

black-series

Sorry for asking, but what exactly is the EGS? It is not the same as the conductor plate, or is it?

alexanderfoti

No the EGS is the Gearbox ECU. On your car, its under the front passenger carpet, clipped in.

Don't be sorry for asking!

black-series

Ok, thanks for the explanation. Your guess concerning the mosfet or driver being faulty does make lots of sense. Regarding the wiring between tcu and gearbox: How could this possibly cause such an error? The communication between the two is via can bus (digital), right? So to my understanding, they either communicate or not. If there was a problem with the wiring, this would most likely throw check sum errors causing the gearbox to go into limp mode. A short circuit in the can line could never cause one specific scenario to happen over and over again while the transmission works fine otherwise. So I would rule this out entirely. Please correct me if I'm wrong here, I am no data bus expert.

alexanderfoti

Thanks.

No, the wiring between the Gearbox ECU(TCU) and the gearbox (conductor plate) is direct. Power to actuate the solenoids and the signals from the sensors inside the gearbox travel along these wires in raw form. The communication between the Gearbox ECU(TCU) and the rest of the car is via canbus.

If there is high resistance in the cable between the Gearbox ECU and the conductor plate, then large current will make it through, but small currents may be attenuated to the point where the solenoid does nothing. The same could be said for a cold solder joint inside the ECU etc.

black-series

Ah, ok, didn't know that. That's the great thing about this forum, you always learn something new about your car.

ecmexchange

It makes so much sense, but it's not something everyone would think about right away. Great piece of advice!

black-series

I don't dare to be too excited yet, but let's put it like this: I am without a shifting fault for the last 180kms I drove.
I decided to swap the EGS and update it to the latest software as well. This was the next logical step and to be honest, more or less one of the last options left. So, alexanderfoti, you were probably right with your guess here.
Great that I managed to draw one of the most unlikely options that could have been the error. The EGS was absolutely no ones first bet. Especially since the car is only 6 years old.
But as I said, I do not want to celebrate too early. So, wish me luck that I do not need to ask for help concerning this particular problem again.
For anyone who might experience a similar problem in the future: Don't rule out the EGS entirely! Before you pay lots of money for a transmission overhaul, swap the EGS first to rule out that option.

I have two questions concerning the adaptation:
Let the car do it on its own or manually do the adaptation process via Xentry? There seem to be different opinions on this topic. (I have EGS53, in case this is relevant)
How long/how many kilometers does it take for a full adaptation and to completely regain the smoothness I was used to?