Diff fluid changes and transfer case

[JCL]

I don't have a copy of the TIS, so I can't provide original references. However, the following are all posted on this site. Credit given to texmin, ripp222, and skeetjunkie:

Posted in response to where to find the TIS reference:

Originally Posted by texmin

Look under:

Repair Instructions / 00 Maintenance and General Data / 0011572 Changing oil in the transfer box (ATC 400/500)

The first line in the document states "When changing the gear oil it is necessary to delete the self-adapting wear values in the transfer box control unit"

I've never cleared the adaptation values since I did the job and have had no problems at all.

texmin wrote up a DIY, found the reference in the TIS, and reported that he never did do it. Not sure if he has done so since.

Posted in reference to how to cleare the VTG fault:

Originally Posted by ripp222

My X5 VTG had the fault logged around 50,000 miles. Here is the relavent SIB:

=====================

SI B27 01 07
Intermediate and Special Transmission
April 2007

Technical Service

SUBJECT

Transfer case (VTG) Fault Code 54C6 Oil wear - Value too high
MODEL
E53 (X5) from 10/03 to 02/05 production
E83 (X3) to 02/05 production
SITUATION
After interrogating the fault memory, as part of an Inspection I or II maintenance service or another repair
requiring a diagnostics procedure, fault code 54C6 Oil wear – Value too high is stored. This fault will not
illuminate a warning lamp.
CAUSE
Transfer case fluid (non lifetime) wear value limit was exceeded.
CORRECTION
Replace the fluid in the transfer case.
PARTS INFORMATION
Part Number Description Quantity
83 22 0 397 244 TF0870 Fluid 1 = 1 liter

Note: Before opening, shake the container to evenly mix the additives in the fluid.

That refers specifically to the VTG fault when the fluid no longer meets spec, not the adaptation values that are to be reset whether or not the fault has been raised.

Posted in a discussion on why it matters:

Originally Posted by skeetjunkie

Additional info from Mike Miller on the resetting the control unit:

The X-Drive transfer case must be reset electronically at the dealership after the oil is changed. You can change the transfer case oil yourself or have it done wherever you want, but the vehicle does have to go back to the dealer to have the transfer case reset. This “resetting” procedure is only possible on the BMW service computer.

Specifically the “reset” uses the actuator inside the transfer case to gauge the thickness of the remaining clutch material. The transfer case then relearns the end stops of the clutch pack to compensate for wear. The electric motor inside the X-Drive transfer case then knows how much it has to apply the clutch pack in order to transfer power when
necessary.

It is that last information from Mike Miller that gives me pause to think. It makes sense that the adaptations are important for future transfer case clutch plate life, not just for a warning as to when the fluid is due to be replaced. Many have posted that they changed the fluid without resetting the adaptations, and it still drove fine. That is certainly possible, but IMO they won't be able to judge their success until they see if the transfer case lasts as long as expected without the adaptations being reset. Incorrect clutch pressures will lead to shortened clutch plate life if too low, and potentially to actuator motor failures if too high.