Well, VTG is the transfer case. The classification resistor is specific to each vehicle and is part of the calibration to allow for production tolerances in clutch plates.

When the transfer case fluid goes out of spec (as determined by the computer measuring the actuator motor position and torque) it needs to be changed.

I do not know whether that specific code is only due to the fluid being out of spec, or whether you have a fault in the actuator motor or wiring harness. A BMW tech would know.

Edit: I have seen references posted to code 54C6 VTG Oil Wear that means change the fluid. I suspect that 54C8 refers to the transfer case clutch plate engagement being out of spec, and it normally has a baseline set by installing a specific classification resistor (which would explain the reference in your code).

This thread has some more background: http://www.xoutpost.com/bmw-sav-foru...sfer-case.html

I believe that you will require BMW service tooling to reset the code, not simply a code reader, after you determine the cause for the code and resolve that problem.

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