11
MOST Bus Diagnosis
Communication Direction in MOST structure
Important!!! The component sequence of the MOST controllers in the ETM is incor-
rect when it comes to signal transmission direction. The correct sequence is indi-
cated above!
The signal transmission direction of the MOST in a vehicle
with full equipment takes place starting at the Control
Display and travels serially towards the CD changer,
Antenna tuner, Hi-fi amplifier, Speech Processing Module,
Navigation, Multi-media Changer, telephone, Audio
System Controller, Instrument Cluster and again back to
the Control Display.
Counts as 2Counts as 2
17
MOST Bus Diagnosis
The Control Display will display a relative node number. This number will indicate how many
modules communicated after the module which set the relative node number of 0.
To find the control module with the relative node number of 0, count from the input side of
the Control Display (counting the Control Display as 0) towards the control modules. When
arriving at the control module with the number as displayed as the relative node number in
the DISplus, the last known communicating module has been found.
Example:
While performing the ring break diagnostics the Control Display has set a relative node
number of 2. Count the Control Display a 0, the Kombi will be 1 and the ASK will be 2.
The ring break occurs between the ASK and the module which precedes it, the telephone
module.
Important
When counting control modules, the multimedia changer (if equipped) and the Nav system
must be counted as two control modules.
In order to perform the count correctly the equipment on the vehicle must first be identified.
When using the MOST network diagram in the DISplus, connector number 1 of the optical
waves are inputs and connector number 2 are outputs.
Module input
Terminal 1
Module output
Terminal 2
Module input
Terminal 1
Module output
Terminal 2
12
Workshop Hint
When preparing to initiate a Ring Break Test it is very important that
the removal and reinstallation of the battery cable be quick and with-
out hesitation.
Hesitation removing or replacing the battery cable may cause volt-
age spikes that will render the Ring Break Test void.
Workshop Hint
For repair of MOST optical wave guide use special tools:
61-4-320 Crimping Tool Kit
Refer to
EPC 61_1578 for specific optical wave guide repair parts.
