This may help to work out the routing and aso find out at what point a break may be:
If a control module in the MOST network stops working and is unable to transmit light pulses onwards, or if there is an open-circuit in the fibre optic cable, the entire MOST network will stop working. This means that all the control modules on the MOST network will stop working. For more information about remedying this, see fault management on the MOST network.
The infotainment control module (ICM) must always be connected on the MOST network for communication on the MOST network to work.
The MOST network connections increase and the signal routing may change when control modules are added because adapter wiring is used to connect the new control module.
The control modules on the MOST network should be positioned in a particular order. If this order is not followed, the fault-tracing of the MOST network will deteriorate.
When further control modules are added to the MOST network, these should be placed in the correct order on the network to make it easier to fault-trace the control modules. If the control modules are connected in another order, this does not effect the function of the MOST network, but fault-tracing will be compromised. The control modules should be placed in the following order:
Infotainment Control Module (ICM) (16/1)
Multimedia module (MMM) (16/108)
CD module (MP2) (16/106)
Phone module (PHM) (16/60)
MD module (MP1) (16/107)
Audio module (AUD) (16/105)
Subwoofer module (SUB) (16/79)
Antenna module (ATM) (16/110).
If the MD module (MP1) is installed as an aftermarket accessory in a car with a phone module (PHM) and CD module (MP2), the MD module (MP1) will change positions with the phone module (PHM).
If the configuration of the MOST network in the car is minimal, the following control modules are connected:
Infotainment control module (ICM)
the audio module (AUD)
the antenna module (ATM).
Ring break diagnostics
General
This function is important when fault-tracing the MOST network. Ring break diagnostics are used when there is an open-circuit in the MOST network and diagnostic trouble code (DTC) ICM-DC02 has been stored in the infotainment control module (ICM).
During fault-tracing, all control modules transmit a message to the infotainment control module (ICM) in reverse order in relation to the position on the network. This means that the aerial module (ATM) is first, not last. The control module which is not working will not transmit an answer to the infotainment control module (ICM). This also means that the control modules connected after the defective control module will be unable to transmit a message to the infotainment control module (ICM).
The same applies in the event of an open-circuit in the fibre optic cable in the MOST network. None of the control modules before the open-circuit will be able to send their message to the infotainment control module (ICM). The infotainment control module (ICM) is then able to calculate the position of the open-circuit from the incoming messages.
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