In the case of a ring fault (defect in the MOST ring), the two MOST control units between which the defect in the ring can be found must be determined first. This is established using the ring fault diagnosis function. However, in the case of some software versions for the CCC, this is not possible for technical reasons (information in the test module 'Ring fault diagnosis'). In this case, the only possibility is to determine the position of the ring fault manually.
”Terminal R” must be switched on for the manual ring fault diagnosis.
To determine the position of the ring fault manually, the MOST connectors must be removed from the individual control units in succession. If red light can be seen in the connector, the MOST connection, starting from Radio2 (or Multi Audio System controller, Car Communication Computer) is OK up to this position.
Search for the ring fault between the first control unit where no light can be seen and the control unit preceding this in the ring.