Originally Posted by MJS
On the servo bikes (and likely the later ones also), the ABS module is responsible for transmitting the speed sensor signal onto the data bus. If you look at the wiring diagram you'll see the speed sensors are connected to the ABS module. Only connection between the ABS unit and the Kombi and ZFE is the data bus.
Interesting that the servo unit can be removed and you still have speedo and odometer then.