MOST system analysis

The MOST bus has a ring structure. This means that a fault in one control unit can have an effect on the entire system. The cause of a system fault = communication fault) in the MOST network is not readily apparent.

The "MOST system analysis" test module (BMW diagnostic system from DIS CD 36) was developed in order to analyze faults in the communication of MOST control units. The MOST system analysis has been improved in DIS-CD 38.

Path details for the "MOST system analysis" test module 

The test module is called up in the DIS (Diagnosis and Information System) as follows:

"Function selection" button -> Complete vehicle -> Body -> Bus functions -> MOST functions -> MOST system analysis.

In order to determine the cause of a system fault in the MOST network the following prerequisites have been established:

• If a communication fault occurs in MOST control units, then this communication fault is not shown in the fault memory of the control unit concerned. This also means that no "x" appears before this control unit in the short test.
• In addition to the list of "really" fitted control units in the short test, a "virtual" control unit appears called "MOST system analysis".

  In this case, "virtual" means that this is not a real control unit, but a wild card for all MOST control units.

• The short test for the "MOST system analysis" "virtual" control unit reads the communication faults of all the MOST control units.
• An "x" in front of this "MOST system analysis" "virtual" control unit indicates that the short test has analyzed one of the following faults:
  • No communication with the following control units:
    1. E60, E61, E63, E64, E87, E90

       CCC or M-ASK: Car communication computer or multi-audio system controller

    2. E65, E66

       CD: Control display

    3. E87, E90

       RAD2: Radio 2 (BMW radio "Professional")

  • MOST ring break
  • Fault in an MOST control unit