I posted this over on RS6.com, sorry for the long post, but hope it might generate some ideas...
The RS6 threw the dreaded 17125 code a few weeks back, although it is intermittent. I was (am) mentally preparing myself for jumping onto the the "new torque converter, new transmission" train. Before going there however I thought I'd do some logging, along the lines of what shoppint reported in http://www.rs6.com/showthread.php/19...l=1#post176023.
In the above link & thread, Tozo noted that the 'Torque Conv Clutch' column is the status of the command to the TC, not the status of the TC itself. I will further speculate that the TCC Solenoid N218 reading is the current drawn by the solenoid as it operates the valve that locks/regulates/opens the clutch. When TC is open, current is low @ 0.048A, when TC is regulating, current varies between 0.4-0.5A, when TC is closed, current is 0.744A
So, some example logs (cleared the 17125 code first!): In general driving, using low/moderate throttle openings, the TC behaved perfectly, opening, regulating, and locking up as expected (ie engine rpm = input rpm). Here's an example log:
[/img]I drove around happily for 30 mins or so in a mix of round town and motorway driving and normal service continued. I checked the error codes, and all clear. Then I got to a nice empty uphill on-ramp to the motorway and gave it full throttle with a kick down, then eased off:
Without posting all of the log, what happened next was that the TC did its normal thing for 20 seconds more, including locking up, and then when I came to a section of road (gentle uphill to flat) where the TC is normally locked at around 100 kph, the TC command status changed to TC OPEN and stayed that way e.g.
You can now see how engine RPM is higher than input RPM and the TC Stall column measures the rev difference (or TC slip speed).
I tried combinations of speeding up, slowing down, even used the paddles to change down/up etc but it stayed open. I then pulled over, and checked the error codes and sure enough 17125 had reappeared. I turned off the engine, let it sit for a minute or so, restarted and drove off. TC back to normal behaviour, opening, regulating and closing.
I managed to repeat this behaviour several times, 'forcing' the TC to apparently stick open by using hard acceleration, then stopping, switching off, and then TC operation went back to normal, locking up properly.
WTF?? It almost seems to me that something other than a failing TC clutch might be at play here. I would have expected if TC clutch was slipping, then the logging symptom would have been to have TC command to be TC CLOSED, while the engine rpm would exceed input rpm (so the solenoid was trying to operate the valve to close the clutch, but there was insufficient pressure to do so, and the clutch would slip etc).
It seems to me that what is going on here is that the command to close the clutch is not evening being registered, so the 'box is behaving like a good old fashioned slush-box without a lock-up clutch at all!!!
Is this a TCU issue instead?? It seems that the solenoid is not even getting the signal to close when it should (check the N218 current alongside the TC command status). Or is it actually the sign of a sticking valve (which I understand from the error code analysis is Pressure Regulating Valve 4), and might a valve body service/refurbish solve the problem??
Or am I waaaaayyy off beam here, and putting the wrong interpretation on all of this. If anyone else has any bright ideas, then I'm listening
) One thing I was never sure about from other torque converter threads on this and other forums - to replace the TC in the C5 RS6, do you need to remove the engine to get at it for replacement?
I took the car into my service shop in Auckland for diagnosis. The car was also throwing 17537 (Fuel trim system too rich, bank 1 and bank 2). I was fully prepared for the bad news of a new TC required. Instead, they found the ATF level was too low by 2L. They topped it up, cleared the codes and took it our for some serious thrashing (since I was getting the code come up after hard acceleration). Result: No codes at all (including the fuel trim code) and TC is locking up just fine.
