Reading Off The Position Of The Open-Circuit

Fig 1: Identifying Ignition ON

Courtesy of VOLVO CARS CORPORATION

Ignition on.

Reading off the result from a ring break diagnostic

The following results can be obtained from a ring break diagnosis:

If the fault occurs when the ring break diagnostic is run, the result will be presented as an open-circuit position.
If there is no fault in the MOST network the result will be OK .
If the Infotainment control module (ICM) gets a signal on the MOST-net, but is unable to decode the signals due to the light intensity being too weak or the signals are too distorted, the result becomes poor signal .
If all control modules on the MOST network believe that they are slave nodes the result is diag all units slave .
If one or several control modules on the MOST-net consider themselves master nodes, the result becomes Diagnosis multimaster .

Read out the open-circuit position from the ring break diagnosis by clicking on the VCT2000 symbol in VIDA (Volvo scan tool). The script also presents a list of all control modules connected to the MOST network.

NOTE:

If the result shows any of the three later alternatives, this must be verified by carrying out the entire test again. Then follow fault tracing for the relevant alternative.

Determining the position of the open-circuit

The Ringbreak diagnostic works so that after the control modules have been powered down and then restarted, the control module on the MOST-circuit that does not receive a light signal sends its address to the Infotainment control module (ICM).

The position of the open-circuit is calculated by working backwards in the MOST network from the infotainment control module (ICM).

All communication occurs clockwise in the loop illustrated.

NOTE:

The ring break diagnostic only counts backwards, irrespective of which or how many control modules are installed in the car. To determine the position of the open-circuit, check the list to, see which control modules are installed in that particular vehicle. Then count backwards following the determined order. The number of control modules can vary between 2 and 7.

HINT: An example is given below.

First open circuit position is indicated by 4. If the MOST configuration is as illustrated, this means that the break is in the Audio module (AUD) or in the cable between Integrated Audio module (AUD) and Television Module (TVM). The open-circuit may even be due to the optical contact in the Television Module (TVM) or in the Integrated Audio module (AUD) being damaged.

In which node is the open-circuit?

Alternative 1

Infotainment Control Module (ICM).

Refer to CHECKING CABLES AND COMPONENTS, INFOTAINMENT CONTROL MODULE (ICM)

Alternative 2

Phone module (PHM)

Audio Control Module (AUD).

Television Module (TVM).

Remote Digital Audio Receiver (RDAR).

Digital Audio Broadcast Module (DABM).

Rear seat entertainment module (RSE)

Integrated audio module (IAM).