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Grantrr: If you are successful in this repair, consider shipping me your old Mech unit, so I may do an "autopsy" to further the knowledge base.
@VAGfan ... Were you ever able to obtain @Olddragger 's Mech for an "autopsy"?
Reason I'm asking, is over the past month, I've started to receive very quick flashes of the yellow “Gearbox fault - Possible no R-gear. Drive on possible” warning. Note that these sporadic warnings slid into the screen (with the warning tone) and very quickly disappeared on their own without the need for me to hit the back arrow on the steering wheel. As of late, It has been observed that these sporadic warnings occur in “stop & go” situations, and not while at speed, i.e., when the clutch temp might actually be rising.
When these warnings started, I checked for codes, with the following two coming up…
P174000 Clutch temperature monitoring P17D800 Torque limitation due to clutch temperature
On only one occasion, the Gearbox Fault warning reappeared, and stayed on screen, which tripped the following CEL (I believe because it was persistent?)
P0700 Fault in transmission control unit
Through all of this, I have experienced zero shifting issues or any loss of reverse gear, which was the warning.
I assume it’s possible the Mechatronics control board might be failing (not properly reading clutch temp, thus the “quick” in and out warnings) and needs replacement? I do know replacement boards can be purchased, and there is an Audi TSB which specifically recommends the PCB 1 and 2 boards be replaced if these clutch temp errors are present. It would be wonderful if the boards were the "smoking gun," and a simple swap out for the updated boards were the fix, but it's the fact the sporadic errors pop up (and disappear) while the car is in slower city traffic which has me concerned that the clutch temps are actually getting too high. But that could also be the fault in the PCB board that necessitated the TSB, correct? Hard to know for sure.
Another course of action, would be to go the Maktrans route and get a renewed Mech valve body only, and swap the TCB from mine, and be done with it. Would just need to find someone local (in Massachusetts) with a PIWIS to perform the various adaptations.
In reviewing receipts provided by the original owner and the dealer, the PDK fluid was changed at appx. 39k miles, and again at 84k miles, so that’s pretty much on schedule. I have 121k on the car now, so it’s due again for a DCTF fluid & filter service. It would be wishful thinking that the fluid is getting "tired" and is causing these issues, but I hate the idea of doing the impending fluid change only, then needing to dump it if this situation persists or gets worse.
Or should I just follow the Audi TSB and perform the prescribed "fix?"
I never got the Mechatronics unit from Olddragger.
The cheapest fix to try is to replace the 2 boards. I would do that first.
Note, that to pull the Mechatronics out, you need to remove the cross-brace beneath the transmission pan. The cross-brace should only be removed when there is no weight on the front-wheels. Also, you need to replace the 6 bolts that fasten the cross-brace, as they are one-time-use torque-to-yield. X-Brace Stretch Bolt Subframe Hardware Kit for B8.5 (Facelift) Models (034motorsport.com)
In the exhaustive reading of forum posts (and YouTube viewing) I've seen on the subject of Mechatronics removal — and it has been non-stop over the past 10-days or so, I have picked up on the requirement to get all-fours off the ground before removing the cross-brace. Now, whether that's in my garage on jack-stands, (Where i would have the time to approach this methodically, and my full compliment of tools, but not the clearance I would like) or at a friend of mine who has a lift (which I'd like to not tie up his lift if issues arise) is unknown at the moment. If I'm only doing the 2 boards and it's successful, I should be able to drive off without the aid of a PIWIS adaptation session, correct?
And thanks much for the link to the crossmember bolt kit; I hadn't added that to my list as of yet!
I never got the Mechatronics unit from Olddragger.
The cheapest fix to try is to replace the 2 boards. I would do that first.
Note, that to pull the Mechatronics out, you need to remove the cross-brace beneath the transmission pan. The cross-brace should only be removed when there is no weight on the front-wheels. Also, you need to replace the 6 bolts that fasten the cross-brace, as they are one-time-use torque-to-yield. X-Brace Stretch Bolt Subframe Hardware Kit for B8.5 (Facelift) Models (034motorsport.com)
You only need to have zero-weight on the front wheels, back does not matter.
No adaptation/calibration needed if just changing the 2 boards.
So the rears can be on stands? That is a plus for sure!
I was under the impression it was a "frame torque thing" which required all wheels off the ground
That makes it a much easier to get the vehicle up a bit more, as I can have the rears on the ramps and use my Rennstands (I only have two) on the front end.
Crossbrace Bolts:
Torque the four hex bolts to 90 Nm (66 Ft lbs) + 135º. Torque the two triple-square bolts to 90 Nm (66 Ft lbs) + 90º
Thanks @VAGfan for all the information provided. I’ll be sure to update this thread after I complete the work. It’s getting a bit chilly up here in New England, so I’ll have to pick and choose a time to tackle this which hopefully syncs with some mild weather.
No adaptation/calibration needed if just changing the 2 boards.
Quick question, if you (or anyone else) knows:
I'm aware that swapping new solenoids into the Mech unit will warrant a visit to the PIWIS for adaptation/calibration.
Does this apply to ALL of the solenoids, or just particular ones? Also, after verifying that the ohm readings on my present solenoids are in spec, can I physically remove them to check/clean the screen filters underneath, and put them back into position without the need for adaptation/calibration? Or does removing them somehow take them out of position?
I think that adaptation may only be needed for replacement of some of the solenoids, but I am not sure which.
Removing, cleaning, and reinstalling the solenoids does not require adaptation/calibration.
I think that adaptation may only be needed for replacement of some of the solenoids, but I am not sure which.
Removing, cleaning, and reinstalling the solenoids does not require adaptation/calibration.
Good to know, thanks.
The condition of the drained fluid along whatever sludge is stuck to the magnets, pan bottom and filters will determine whether or not I decide to take the cleaning aspect of this impending project to Level II...
Three weeks ago, I purchased a 2015 Macan Turbo with 85k and good looking CarFax. I washed it, drove it for 2 miles, and then up popped the engine fault and gearbox codes. Turns out the mechatronic was replaced by an Indie and programmed by Porsche Austin in May. The 'repair' worked for 40 miles and then problems returned. The owner sold it to a guy that owns a repair shop and has an active auto dealer license TX. Porsche Austin gave him the 25k+ number so this unscrupulous sack of excrement tried to sell it on his car lot for months. When that failed, he sent it to Copart (without disclosure) to hook the next sucker (me). This thread has been exceptionally informative. I happen to be equidistant to GT Peace Auto (VA) and ATLSpeedWerks (GA). Wish me luck. I have the Porsche Austin records and I have to contact the Indie shop again to get all the details about their repair work. He gave me the 411 on the previous owner but wants to stay out of the picture because apparently some people play rough in TX.
Porsche owner for less than 3 weeks which if I replace the tranny gives me a TCO approaching $20k per week. I should have taken up a drug habit. It would have been cheaper.
I have new pictures of my old mechatronic unit that better illustrates the damage that occurred. One can see the melting and the scoring of the hard plastic. The picture of the bottom part of the unit clearly shows how the plastic particles contaminated the fluid. The heat had to be substantial.
Just got the car and other transmission home. Now when work allows I have to get everything set up. Car raised, disassemble the donor transmission, flush my old lines and cooler very well, then reassemble. I will try to take pics along with the process. I also want to take the old circuit board apart and see if there is any hint within as to what went wrong.
Please note the Audi markings!
Why would you ever put a plastic part in a hot working environment let alone the most critical one that would take serious amount of effort and cost to detect and remedy? I've seen BMW doing this in the 2000s with water pump and now Porsche/VW/Audi. WTH are they thinking?
I am far from being the expert in these matters although I am fairly well educated concerning heat and engines etc. I am sure there was a reason but I don't understand why they placed the tcu inside the transmission anyway? Heat is a serious enemy toward electronics. Mute point ....it doesn't change anything for my situation....unless I do decided to run a divorced cooler. Not only do these electronics have to take the heat they also have to deal with the forces of 7-8 liters of fluid being tossed around. What do y'all think about overfilling?
I designed IC chips for a living and it made me cringed whenever I see circuit board like this a mechanically hot working condition. All these circuit behave totally different across the temperature spectrum, especially the high temp with fluctuation. I'm pretty sure whoever design this did not test it properly. Each chip has different failure rate at different tempurature and the probability for one of many of them to fail is exponentially high. It doesn't take much to malfucntion when 1 of them fail and worse, it increase over time due to tempurature cycling causing degradation. There's a reason that the ECU of the car is rarely changed hardware wise and it is located in the best location inside the car.
12-05-2023, 10:45 AM
