Faulty Signal
No communication
951 2867 MOST instrumentation 951 2867 MOST instrumentation
Checking the wiring and component
The infotainment control module (ICM) has detected an open-circuit in communication on 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, for any reason, a control module is unable to handle (receive or transmit) signals onwards on the MOST network, or if there is an open-circuit in the fiber optic cable, the infotainment control module (ICM) will shut down all functionality.
Communication on the fiber optic net is one-directional. The control modules on the MOST network receive light signals, amplify them and then send them onwards. 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 either be caused by interference when starting the MOST network, or by intermittent faults in the power supply/ground for one of the control modules in the network. The fault is evaluated depending on how it occurs. If the fault recurs, fault-trace for permanent faults.
It can be difficult to diagnose intermittent faults using a ring break diagnostic because for this to work the fault must occur during the diagnostic.
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
Ring break diagnostic
A ring break diagnostic should be run to determine whether the fault has occurred.
To carry out a full ring break diagnostic of the MOST system, proceed as follows:
1. Switch off the ignition and remove the key
2. Connect separate external voltage feed to the communication tool.
3. Disconnect the battery negative lead. Battery, disconnecting Battery, Disconnecting
4. Wait 1 minute.
5. Ignition switch position II.
6. Connect the battery negative terminal.
7. Wait at least 30 seconds after switching on the ignition before reading off the position of the open-circuit.
Other information:
- For information about fuses, see the wiring diagram.
- For information on battery location: Battery, replacing Removal and Replacement
Continue - Reading off the position of the open-circuit
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Checking cable and component
If the result of the ring break diagnostic is POOR, 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 the ring break diagnostic is OK, the fault is intermittent.
Fault-tracing using the ring break diagnostic assumes that the fault is permanent or active when the test is run, i.e. the system is powered having been off.
Hint: If diagnostic trouble code (DTC) ICM-DC01 is intermittent, read off the status of the ring break diagnostic from the frozen values in Vehicle communication.
Check the communication on the MOST network by bypassing the control modules one by one on the MOST network 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
- Ignition on
- Activate the infotainment system
- Check that the communication on the MOST network is functioning by reading off the status of the MOST locked parameter for at least 30 seconds. The parameter indicates whether the MOST network is closed and communication possible. Click the VCT2000 symbol to read off the status of the MOST network.
If the communication on the MOST network is stable when a control module is disconnected, check the power supply and the ground terminal on the relevant control module. Check for intermittent faults. Try replacing the component if no fault is found.
Continue - Verification
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Reading off the position of the open-circuit
- Ignition on.
Reading off the result from a ring break diagnostic
Click the VCT2000 symbol to read off the result of the ring break diagnostic.
As well as the result from the ring break diagnostic, a list of the control modules included in the MOST network is provided for that car.
Note! The figure shows the MOST-net with maximum number of possible control modules. The number of control modules can vary between 2 and 6.
The following results can be obtained from a ring break diagnosis:
- If the diagnostic indicates an open-circuit in the communication on the MOST network, the result will be an open-circuit position
- The result will be OK if there is no fault on the MOST network Continue by selecting option 3 below.
- If the infotainment control module (ICM) receives a signal on the MOST network but is unable to decode it because the luminance is weak or the signals are distorted, the result will be POOR. Continue by selecting option 3 below.
Determining the position of the open-circuit
The position of the open-circuit is calculated by working backwards in the MOST network from the infotainment control module (ICM).
Note! The ring break diagnostic always counts backwards, irrespective of which, or how many control modules, are installed in the vehicle. 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 6.
Two examples are outlined below:
- First open circuit position is indicated by 1. This means that the open circuit is in the Integrated Audio Module (IAM) or in the cable between the Bluetooth phone module (BPM) and the Integrated Audio Module (IAM).
- First open circuit position is indicated by 3. This means that the open circuit is in the Audio module (AUD) or in the cable between the Audio module (AUD) and the Multimedia module (MMM). The open circuit may be caused by a damaged optical connector in the Multimedia module (MMM). This means that Multimedia module (MMM) cannot interpret the incoming signal from Audio module (AUD).
Select the alternative for the control module to be checked.
Alternative 1
Remote Digital Audio Receiver (RDAR).
Audio module (AUD)
Integrated audio module (IAM).
Alternative 2
Phone module (PHM)
Bluetooth phone module (BPM).
Multimedia module (MMM)
Infotainment control module (ICM)
Alternative 3:
The result from the ring break diagnostic indicates that the MOST network is OK.
The result from the ring break diagnostic is POOR.
Other information:
- Location of components Component Location, Infotainment
Select an alternative.
1 - Checking cable and component
2 - Checking cable and component
3 - Checking cable and component
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Checking cable and component
Select the control module to be checked from the list.
1. Remote Digital Audio Receiver (RDAR).
2. Audio Control Module (AUD).
3. Integrated audio module (IAM).
Select the control module.
1 - Checking cable and component
2 - Checking cable and component
3 - Checking cable and component
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Checking cable and component
Select the control module to be checked from the list.
1. Phone module (PHM)
2. Bluetooth phone module (BPM).
3. Multimedia module (MMM).
4. Infotainment Control Module (ICM).
Select the control module.
1 - Checking cable and component
2 - Checking cable and component
3 - Checking cable and component
4 - Checking cable and component
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Checking cable and component
Checking the fault cause
Check the fault cause as follows:
1. Ignition off
2. Disconnect the MOST connector from Remote Digital Audio Receiver (RDAR).
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 network is functioning by reading off the status of the MOST locked parameter for at least 30 seconds. The parameter indicates whether the MOST network is closed and communication possible Click the VCT2000 symbol to read off the status of the MOST network.
7. If the parameter displays that the MOST network is not correctly connected, check the receiving control module in the same way as above.
The communication on the MOST network is working if the menu text is displayed. The cause of the fault is then in the Remote Digital Audio Receiver (RDAR). 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 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 the power supply and ground connection for the Remote Digital Audio Receiver (RDAR).
- Check the MOST connection. Check for dirt, loose connections and damage
- If no fault is found, replace the Remote Digital Audio Receiver (RDAR).
Remedy as necessary.
Other information:
- Signal specification Pinout Values and Diagnostic Parameters
- Optical wiring harness check
- Fiber optic cable harness, repairing Fiber Optic Cable Harness, Repairing
- Location of components Component Location, Infotainment
- Satellite radio control module Satellite Radio Control Module
Continue - Verification
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Checking cable and component
Checking the fault cause
Check the fault cause as follows:
1. Ignition off
2. Disconnect the MOST connector from the audio module (AUD)
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 network is functioning by reading off the status of the MOST locked parameter for at least 30 seconds. The parameter indicates whether the MOST network is closed and communication possible Click the VCT2000 symbol to read off the status of the MOST network.
7. If the parameter displays that the MOST network is not correctly connected, check the receiving control module in the same way as above.
The communication on the MOST network is working if the menu text is displayed. If this is the case, the fault cause is in the audio module (AUD). 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 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 the power supply and the ground terminal for the audio module (AUD)
- Check the MOST connection. Check for dirt, loose connections and damage
- Replace the audio module (AUD) if no fault is found.
Remedy as necessary.
Other information:
- Audio module (AUD), replacing Audio Module (AUD), Replacing
- Checking the voltage / ground terminal Checking Voltage / Ground Connection
- Signal specification Signal Specification, Audio Module (AUD)
- Fiber optic cable harness, repairing Fiber Optic Cable Harness, Repairing
- Optical wiring harness check
- Location of components Component Location, Infotainment
Continue - Verification
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Checking cable and component
Checking the fault cause
Check the fault cause as follows:
1. Ignition off
2. Unplug the MOST connector from the integrated audio module (IAM).
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 network is functioning by reading off the status of the MOST locked parameter for at least 30 seconds. The parameter indicates whether the MOST network is closed and communication possible Click the VCT2000 symbol to read off the status of the MOST network.
7. If the parameter displays that the MOST network is not correctly connected, check the receiving control module in the same way as above.
The communication on the MOST network is working if the menu text is displayed. If this is the case, the fault cause is in the integrated audio module (IAM). 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 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 the integrated audio module (IAM) power supply and ground connection.
- Check the MOST connection. Check for dirt, loose connections and damage
- If no fault can be found, change the integrated audio module (IAM).
Remedy as necessary.
Other information:
- Checking the supply voltage/ground terminal Checking Supply Voltage/Ground Terminal, Integrated Audio Module (IAM)
- Signal specification Signal Specification, Integrated Audio Module (IAM)
- Fiber optic cable harness, repairing Fiber Optic Cable Harness, Repairing
- Optical wiring harness check
- Location of components Component Location, Infotainment
Continue - Verification
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Checking cable and component
Checking the fault cause
Check the fault cause as follows:
1. Ignition off
2. Disconnect the MOST connector from the phone module (PHM)
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 network is functioning by reading off the status of the MOST locked parameter for at least 30 seconds. The parameter indicates whether the MOST network is closed and communication possible Click the VCT2000 symbol to read off the status of the MOST network.
7. If the parameter displays that the MOST network is not correctly connected, check the receiving control module in the same way as above.
The communication on the MOST network is working if the menu text is displayed. If this is the case, the fault cause is in the phone module (PHM). 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 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 the power supply and the ground terminal for the phone module (PHM)
- Check the MOST connection. Check for dirt, loose connections and damage
- Replace the phone module (PHM) if no fault is found.
Remedy as necessary.
Other information:
- Checking voltage / ground connection Checking Voltage / Ground Connection
- Signal specification Signal Specification
- Fiber optic cable harness, repairing Fiber Optic Cable Harness, Repairing
- Optical wiring harness check
- Location of components Component Location, Infotainment
Continue - Verification
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Checking cable and component
Checking the fault cause
Check the fault cause as follows:
1. Ignition off
2. Unplug the MOST connector from the Bluetooth phone module (BPM).
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 network is functioning by reading off the status of the MOST locked parameter for at least 30 seconds. The parameter indicates whether the MOST network is closed and communication possible Click the VCT2000 symbol to read off the status of the MOST network.
7. If the parameter displays that the MOST network is not correctly connected, check the receiving control module in the same way as above.
The communication on the MOST network is working if the menu text is displayed. If this is the case, the fault cause is in the global positioning system module (GPS). 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 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 the global positioning system module (GPS) power supply and ground connection.
- Check the MOST connection. Check for dirt, loose connections and damage
- If no fault can be found, change the global positioning system module (GPS).
Remedy as necessary.
Other information:
- Checking the supply voltage/ground terminal Component Tests and General Diagnostics
- Signal specification Signal Specification, Bluetooth Phone Module (BPM)
- Fiber optic cable harness, repairing Fiber Optic Cable Harness, Repairing
- Optical wiring harness check
- Location of components Component Location, Infotainment
Continue - Verification
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Checking cable and component
Checking the fault cause
Check the fault cause as follows:
1. Ignition off
2. Disconnect the MOST connector from the multimedia module (MMM)
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 network is functioning by reading off the status of the MOST locked parameter for at least 30 seconds. The parameter indicates whether the MOST network is closed and communication possible Click the VCT2000 symbol to read off the status of the MOST network.
7. If the parameter displays that the MOST network is not correctly connected, check the receiving control module in the same way as above.
The communication on the MOST network is working if the menu text is displayed. If this is the case, the fault cause is in the multimedia module (MMM). 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 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 the power supply and the ground terminal for the multimedia module (MMM)
- Check the MOST connection. Check for dirt, loose connections and damage
- Replace the multimedia module (MMM) if no fault is found.
Remedy as necessary.
Other information:
- Multimedia module (MMM), replacing Multimedia Module (MMM), Replacing
- Checking the voltage / ground terminal Checking Supply Voltage/Ground Terminal, Multimedia Module (MMM)
- Signal specification Signal Specification, Multimedia Module (MMM)
- Fiber optic cable harness, repairing Fiber Optic Cable Harness, Repairing
- Optical wiring harness check
- Location of components Component Location, Infotainment
Continue - Verification
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Checking cable and component
- 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.
The control module is defective if the infotainment control module (ICM) is not emitting light.
If the infotainment control module (ICM) is transmitting light, the fault is in the MOST cable for the next control module.
Check the MOST connection. Check for dirt, loose connections and damage.
Replace the MOST cable if no fault is found in the MOST terminal.
Remedy as necessary.
Other information:
- Fiber optic cable harness, repairing Fiber Optic Cable Harness, Repairing
- Location of components Component Location, Infotainment
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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VERIFIED - FAULT FOUND
VERIFICATION FAILED - Fault-tracing information
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Fault-tracing information
Attempt New Test - Checking the wiring and component
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