Part 1
Fault-tracing
Information
The infotainment control module (ICM) has detected an open-circuit in the MOST network. The MOST network is a fiber optic ring network. This means that all control modules which are connected to the network must be powered and grounded for the infotainment system to work. If a control module for any reason is unable to receive or send signals on the MOST-net or if there is an open circuit on the fiber-optic line, then Infotainment control module (ICM) will shut off all functionality.
Communication on the fiber optic net is one-directional. The control modules on the MOST-net receive the light signals, amplify them and then send them on. The MOST connectors for the control modules contain two fiber optic cables, one for incoming and one for outgoing signals.
If the fault is intermittent, it has been registered previously but is no longer present. Intermittent faults can be caused by interference at start up of the MOST network (ECM) or can be a different type of fault which occurs on different occasions. The fault is evaluated depending on how it occurs. If the fault recurs, fault-trace for permanent faults.
An intermittent fault may be difficult to diagnose using ring break diagnosis because a condition for this is that the fault occurs while the diagnostics program is running. If the fault is permanent, perform a ring break diagnostic to locate the open-circuit.
Continue - Checking for open-circuits
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Checking for open-circuits
A ring break diagnosis should be performed to determine where the fault has occurred. Troubleshooting with ring break diagnosis requires that the malfunction is permanent or active while the test is running (when the system is supplied with voltage after having been without voltage) Get the MOST system to perform a complete ring break diagnosis, as follows:
1. Ignition switch position II.
2. Remove fuse 11C/1 (40 A).
3. Wait 30 seconds.
4. Reinstall fuse 11C/1.
5. Wait at least 30 seconds before reading out interruption position.
Hint: Fuse 11C/1 is located in the distribution box under the glovebox.
Other information
- For information about fuses, see the wiring diagram.
Continue - Reading off the position of the open-circuit
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Reading off the position of the open-circuit
- Ignition on.
Reading off the result from a ring break diagnostic
The following results can be obtained from a ring break diagnosis:
1. If the fault occurs when the ring break diagnostic is run, the result will be presented as an open-circuit position.
2. If there is no fault in the MOST network the result will be OK.
3. 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.
4. If all control modules on the MOST network believe that they are slave nodes the result is diag all units slave.
5. 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. 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 Ring break 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).
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).
Alternative 3
The result from the ring break diagnostic indicates that the MOST network is OK.
The result from the ring break diagnostic displays a poor signal.
The result from the ring break-diagnosis shows diagnosis multimaster.
Alternative 4
The result from the ring break-diagnosis shows diagnosis all units slave.
Select one of the above options.
1 - Checking cables and components, Infotainment control module (ICM)
2 - No communication
3 - Checking the cable and component
4 - Checking the infotainment control module (ICM)
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Checking cables and components, Infotainment control module (ICM)
- Ignition off.
- Disconnect the MOST cable connector from the infotainment control module (ICM).
- Ignition on.
- Activate the infotainment system.
Check visually whether the infotainment control module (ICM) is emitting light from the MOST connector. If no light is emitted by the infotainment control module (ICM) then the control module is damaged.
If the infotainment control module (ICM) is transmitting light, the fault is in the MOST cable for the next control module.
Remedy as necessary.
Other information
- Information and Entertainment Display Service and Repair
- Checking the supply voltage/ground terminal Component Tests and General Diagnostics
- Diagnostic Instructions - Fibre Optic Cable Diagnostic Instructions - Fibre Optic Cable
- Location of components Component Location, Infotainment Control Module (ICM)
Continue - Verification
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Verification
Verification
Hint: After carrying out the repair, check that the fault has been remedied.
- Ignition off
- Reinstall the connectors, components etc.
- Ignition on.
Activate the infotainment system and select the radio.
Check whether there is sound from the radio in the loudspeakers.
Is the sound of the radio coming through the loudspeakers?
Yes - VERIFIED
No - VERIFICATION FAILED
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VERIFICATION FAILED - Fault-tracing information
VERIFIED - FAULT FOUND
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Fault-tracing information
Information
Fault-tracing information
The fault should have been detected and remedied. As this is not the case fault-tracing has failed.
Exit fault-tracing for this diagnostic trouble code (DTC) or make another attempt.
Do you want to exit fault-tracing?
Yes - Exit fault-tracing
No - Attempt New Test
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Attempt New Test - Information
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Checking the cable and component
Troubleshooting with ring break diagnosis requires that the malfunction is permanent or active while the test is running (when the system is supplied with voltage after having been without voltage)
If the result from the ring break diagnostic is OK, the fault is intermittent. Skip remaining Troubleshooting by selecting Continue.
If the result of the ring break diagnostic is poor signal, the infotainment control module (ICM) is receiving a signal on the MOST network. However, it is unable to decode the signals because the luminance of the signals is too weak or the signals are distorted.
If the result from ring break diagnosis is diagnosis multimaster this indicates that one or several control modules consider themselves master node on the MOST-net.
Hint: If diagnostic trouble code ICM-U1A1587 is generated intermittently, obtain a ring break diagnosis status reading in Vehicle Communication frozen values.
Bypass the control modules on the MOST network one at a time to check network communication. Proceed as follows:
- Ignition off.
- Disconnect the MOST connector from the relevant control module.
- Connect the MOST cable to special tool: 951 2867 MOST instrumentation 951 2867 MOST Instrumentation
- Activate the infotainment system.
- Check that the communication on the MOST-net works by reading out the status for the parameter MOST locked for at least 30 seconds. Click on the VCT2000 symbol to read out status on MOST-net. The parameter indicates whether the MOST network is closed and communication possible.
If communication on the MOST-net is stable when a control module is disconnected, check voltage feed and ground connection for the control module in question for intermittent malfunctions. Try replacing the component if no fault is found.
Continue - Verification
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Checking the infotainment control module (ICM)
The malfunction was caused by an internal error in Infotainment control module (ICM).
Continue the fault-tracing therefore by reading off diagnostic trouble codes (DTCs) from the infotainment control module (ICM) and then following the relevant fault-tracing procedures. Then go back and troubleshoot using ring break-diagnosis.
Continue - DONE
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No communication
Checking the cable and component
Select the control module to be checked from the list.
1. Phone module (PHM)
2. Audio Control Module (AUD).
3. Television Module (TVM).
4. Remote Digital Audio Receiver (RDAR).
5. Digital Audio Broadcast Module (DABM).
6. Rear seat entertainment module (RSE)
7. Integrated audio module (IAM).
Select the control module.
1 - Checking phone module (PHM)
2 - Checking Audio module (AUD)
3 - Checking Television Module (TVM).
4 - Checking the Remote Digital Audio Receiver (RDAR)
5 - Checking the Digital Audio Broadcast Module (DABM)
6 - Checking rear seat entertainment module (RSE)
7 - Checking Integrated Audio Module (IAM)
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Checking Audio module (AUD)
Checking fuses
Check that the fuse for the function in question is intact.
Replace the fuse if it is damaged.
For information about fuses, see the wiring diagram.
Checking the fault cause
Check the fault cause as follows:
1. Ignition off.
2. Disconnect the MOST connector from the relevant control module.
3. Connect the MOST cable to special tool: 951 2867 MOST instrumentation 951 2867 MOST Instrumentation
4. Ignition on.
5. Activate the infotainment system.
6. Check that the communication on the MOST-net works by reading out the status for the parameter MOST locked for at least 30 seconds. The parameter indicates whether the MOST network is closed and communication possible.
7. If the parameter shows that the MOST network is not closed, check the receiving control module in the same way as described above.
The communication on the MOST network is working if the menu text is displayed. Then the malfunction cause is in the control module in question. Continue the fault-tracing by checking the component. The communication on the MOST network is not working if the menu text is not displayed. The fault cause is then in the MOST cable for the next control module. Continue the fault-tracing by checking the fiber optic cable.
Checking the cable
- Check the MOST connection. Check for dirt, loose connections and damage.
- Replace the MOST cable if no fault is found in the MOST terminal.
Checking the component
- Check voltage feed and ground connection for the control module in question.
- Check the MOST connection. Check for dirt, loose connections and damage.
- Replace the control module if no fault is found.
Click on the VCT2000 symbol to read out status on MOST-net.
Note! To read off the open circuit position again and verify that the MOST loop is closed or if there is another open circuit in the loop, the MOST system must complete a complete ring break-diagnosis as previously in the fault tracing (i.e. the MOST system is supplied with voltage after having been without power).
Remedy as necessary.
Other information
- Audio Module Audio Module
- Signal description, audio module (AUD) Signal Description, Audio Module (AUD)
- Component location, audio module (AUD) Component Location, Audio Module (AUD)
- Diagnostic Instructions - Fibre Optic Cable Diagnostic Instructions - Fibre Optic Cable
Continue - Verification
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Checking Integrated Audio Module (IAM)
Checking fuses
Check that the fuse for the function in question is intact.
Replace the fuse if it is damaged.
For information about fuses, see the wiring diagram.
Checking the fault cause
Check the fault cause as follows:
1. Ignition off.
2. Disconnect the MOST connector from the relevant control module.
3. Connect the MOST cable to special tool: 951 2867 MOST instrumentation 951 2867 MOST Instrumentation
4. Ignition on.
5. Activate the infotainment system.
6. Check that the communication on the MOST-net works by reading out the status for the parameter MOST locked for at least 30 seconds. The parameter indicates whether the MOST network is closed and communication possible.
7. If the parameter shows that the MOST network is not closed, check the receiving control module in the same way as described above.
The communication on the MOST network is working if the menu text is displayed. Then the malfunction cause is in the control module in question. Continue the fault-tracing by checking the component. The communication on the MOST network is not working if the menu text is not displayed. The fault cause is then in the MOST cable for the next control module. Continue the fault-tracing by checking the fiber optic cable.
Checking the cable
- Check the MOST connection. Check for dirt, loose connections and damage.
- Replace the MOST cable if no fault is found in the MOST terminal.
Checking the component
- Check voltage feed and ground connection for the control module in question.
- Check the MOST connection. Check for dirt, loose connections and damage.
- Replace the control module if no fault is found.
Click on the VCT2000 symbol to read out status on MOST-net.
Note! To read off the open circuit position again and verify that the MOST loop is closed or if there is another open circuit in the loop, the MOST system must complete a complete ring break-diagnosis as previously in the fault tracing (i.e. the MOST system is supplied with voltage after having been without power).
Remedy as necessary.
Other information
- General audio player module Service and Repair
- Checking the supply voltage/ground terminal Component Tests and General Diagnostics
- Signal description, Integrated Audio Module (IAM) Signal Description, Integrated Audio Module (IAM)
- Diagnostic Instructions - Fibre Optic Cable Diagnostic Instructions - Fibre Optic Cable
- Location of components Component Location, Integrated Audio Module (IAM)
Continue - Verification