The MOST (Media Oriented Systems Transport) network uses a ring bus for data communication between the various control units. Signal transmission is by means of fibre-optic cable. Data transmission on the ring bus takes place in one direction only. On the MOST network, messages can only be transmitted provided the bus ring is complete and fully functional. If there is a ring fault in the MOST network, however, the diagnosis system can only communicate with the instrument cluster and the Control Display. This is possible because those two control units are directly connected to the K-CAN SYSTEM bus.
If, for example, the power supply or the diode of a control unit is defective, it is no longer possible to communicate with the control units on the MOST bus. Exceptions here are of course the instrument cluster and the Control Display.
Transmission of messages is from the Control Display towards the CD changer, ..., instrument cluster, ... and back to the Control Display.
At the testing device, switch to function selection. The test program for the optical check of the MOST bus can be selected at Body, Bus Functions, MOST Functions and Optical Test.