Viano transfer case issue and ABS fault

Oh dear, transfer case issues are never fun! Based on your description, the ABS system link is plausible. When the ABS control module detects an issue, it can indeed throw other systems, like the transfer case, into disarray as a protective measure. First things first, have you had the fault codes read? Knowing the diagnostic trouble codes (DTCs) stored in the system will be incredibly helpful. Specifically, I would look for codes related to the ABS, traction control, and the transfer case itself. Even seemingly unrelated codes can provide clues. Knowing the exact codes will give us a much clearer picture of what's going on. A generic OBD2 scanner might pick up some codes, but a Mercedes-specific diagnostic tool would be ideal for a comprehensive scan.

Thanks for the quick response. I haven't read the fault codes myself, but is it possible for faulty ABS sensors to trigger the transfer case limp mode, even if the transfer case itself is mechanically sound?

Absolutely, a faulty ABS sensor is a prime suspect! The traction control system relies heavily on accurate wheel speed data from those sensors. If one or more sensors are giving incorrect readings, the control module might interpret this as a loss of traction, and in an attempt to stabilize the vehicle, it could engage the transfer case limp mode, or even disable certain gears. The system is designed to err on the side of caution. It is highly recommended that you get a diagnostic scan done as soon as possible. I would suggest that you visit a workshop to identify the fault codes that are saved in the system. This should provide a clearer picture and help you to diagnose the issue. Better safe than sorry!

Thanks for the advice. I took it to a workshop and it turned out to be a faulty ABS sensor, just as you suggested. Replaced it, cleared the fault codes, and everything is running smoothly again. The total repair cost was 0€ as it was still under warranty.