5HP19 Torque Converter

[rawfuls]

Actually have an '03 Z4 3.0i M54, but basically an E46 power-plant.
Got a dreaded P0700 a P0741, 'Transmission Control System (MIL Request)' and 'Torque Converter Clutch Circuit Performance/Stuck Off' respectively. Car drives fine, TQ doesn't feel noticeably bad or like it's slipping at all.


Auto trans was initially drained and filled with Redline D4 ATF for the first time in it's lifetime at 112, 133 miles - no issues before, but wanted to do preventative. Most forums say D4 is perfectly compatible with Esso and lots of good posts with people running Redline D4 over Esso.
Got the codes around 115k, cleared and reset- didn't come back until yesterday at 118k.
Cleared and reset, drove to work this morning- no issues.


Looking for thoughts, looks like most people say Esso/D4 is suitable, thinking maybe I should drain and fill with Esso fluids (again) to see if I can counter the o-ring in the TQ that's failing, or if it's just impending doom of the TQ.
If it's impending doom of the TQ, most shops are looking for ~$1,200 in the SoCal Inland Empire area.
Doesn't look like something that's very DIY friendly.


I'd love a manual, but that's just not in the cards at the moment

[whiskychaser]

I think your diagnosis is likely to be correct. But this article gives you a couple of other things which might just be the cause. Could be worth a look as they don't involve removing the trans.
https://blog.bavauto.com/11812/bmw-t...verter-clutch/

You have probably read this too but check out post 11 about a service bulletin here:
https://www.bimmerforums.com/forum/s...h-circuit-open

[rawfuls]

I think your diagnosis is likely to be correct. But this article gives you a couple of other things which might just be the cause. Could be worth a look as they don't involve removing the trans.
https://blog.bavauto.com/11812/bmw-t...verter-clutch/

You have probably read this too but check out post 11 about a service bulletin here:
https://www.bimmerforums.com/forum/s...h-circuit-open

Yeah, I'm curious to think maybe the Redline D4 caused the turbine shaft seal to deteriorate at a more rapid rate due to the properties it may have as opposed to the Esso LT OEM fluid.
Despite hundreds of successful Redline D4 fluid swaps, I think I may start inquiring about some OEM fluid and doing a filter/gasket replacement to try and get rid as much of the D4 fluid as possible.

Alternatively, I am also thinking of just running the TQ until it fails completely, since it's showing 0 signs of slip, when it locks up.
Introducing fresh fluids could upset the shaft seal yet again, and if the fluid needs to be replaced when the TQ is removed, then...