Since this is a topic/technical issue which will require replies, and not a "New Member Introduction", this thread has been moved to the model specific forum.

 

I don't imagine we'll find much meaningful data on troubleshooting it.

Here is what little I can dig up"

It is powered off fuse #18, along with tons of other stuff, including your Navigation display unit, so I doubt that is the cause.
It is grounded to point G401, which includes your trunk lid opener main switch, and the audio HVAC display, so again, sounds doubtful.

Looks like it puts out 0-5V pulses when working, outputs them on a white wire pin 26 on main radio/ nav system. If its open or shorted, it no workie.

The interface dial has a 5 pin connector with 4 wires,
1 - white 0-5v pulses, as noted above
2 - gray shield ground for above
3 - Blk ground for pin #1
4 - purple power supply to unit, powered off fuse #18

Looks like there is a process to check it out on board, but too detailed to read now. More later.

 

The check is, with key on
make sure you have voltage on Pin 4 (12V to Ground) (no=bad)
Ground Pin3 (0V to ground) (no=-bad)

Turn off car,
check for continuity between Pin 1 of interface dial and Pin 26 of audio Nav unit (no = bad)
Check for continuity between pin 13 & 26 (yes = bad)

IF all those are good, your dial is bad

Dang, more than I expected to find when I dove into this. Good luck