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. 

HINT: Note that the antenna module (ATM) is not normally included in a ring break diagnostic if the fuse is not removed. This means that the position of the open-circuit moves one step backwards in the MOST network. 

HINT: On fully equipped vehicles, if the open-circuit position is 0, this may be because of: 

• Subwoofer module (SUB)
• The fiber optic cable between the subwoofer module (SUB) and the antenna module (ATM)
• Antenna module (ATM)
• The fiber optic cable between the antenna module (ATM) and the infotainment control module (ICM)
• The optical connector in the infotainment control module (ICM). This means that the infotainment control module (ICM) is not able to interpret the incoming signal correctly.

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 see 9512867
• 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.

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.

Click the VCT2000 symbol to read off the status of the MOST network.

• Continue 

  Refer to VERIFICATION 

Select the control module to be checked from the list.

1. Antenna module (ATM)

2. Subwoofer module (SUB)

3. Audio module (AUD)

4. CD player module (MP2)

Select the control module. 

• 1 

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• 2 

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• 3 

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• 4 

  Refer to CHECKING CABLE AND COMPONENT 

Select the control module to be checked from the list.

1. Phone module (PHM)

2. MD player module (MP1)

3. Multimedia module (MMM)

4. Infotainment control module (ICM)

Select the control module. 

• 1 

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• 2 

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• 3 

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• 4 

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Checking the fault cause 

Check the fault cause as follows:

1. Ignition off
2. Disconnect the MOST connector from the antenna module (ATM)
3. Connect the MOST cable to special tool see 9512867
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
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 antenna module (ATM). 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 antenna module (ATM)
• Check the MOST connection. Check for dirt, loose connections and damage
• Replace the antenna module (ATM) if no fault is found.

Remedy as necessary.

Click the VCT2000 symbol to read off the status of the MOST network.

Other information: 

• To access or replace the antenna module (ATM), see RECEIVER GPS, TMC (ATM), REPLACE
• For information about checking the power supply and ground terminal, see CHECKING THE POWER SUPPLY AND GROUND TERMINALS
• For information about signals, see SIGNAL SPECIFICATION
• see OPTICAL WIRING HARNESS CHECK
• For information about checking and replacing the MOST cable, see FIBER OPTIC CABLE HARNESS, REPAIRING
• For information about location and order of control modules in the MOST network, see LOCATION OF COMPONENTS .

Select continue. 

• Continue 

  Refer to VERIFICATION 

Checking the fault cause 

Check the fault cause as follows:

1. Ignition off
2. Disconnect the MOST connector from the subwoofer module (SUB)
3. Connect the MOST cable to special tool see 9512867
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
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 bypassed control module. 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 subwoofer module (SUB)
• Check the MOST connection. Check for dirt, loose connections and damage
• Replace the subwoofer module (SUB) if no fault is found.

Click the VCT2000 symbol to read off the status of the MOST network.

Remedy as necessary.

Other information: 

• To access or replace the subwoofer module (SUB), see SUBWOOFER MODULE (SUB), REPLACING
• For information about checking the power supply and ground terminal, see CHECKING THE VOLTAGE / GROUND TERMINAL
• For information about signals, see SIGNAL SPECIFICATION
• For information about checking and replacing the MOST cable, see FIBER OPTIC CABLE HARNESS, REPAIRING
• see OPTICAL WIRING HARNESS CHECK
• For information about location and order of control modules in the MOST network, see LOCATION OF COMPONENTS .

• Continue 

  Refer to VERIFICATION 

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 see 9512867
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
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.

Click the VCT2000 symbol to read off the status of the MOST network.

Remedy as necessary.

Other information: 

• To access or replace the audio module (AUD), see AUDIO MODULE (AUD), REPLACING
• For information about checking the power supply and ground terminal, see CHECKING THE VOLTAGE / GROUND TERMINAL
• For information about signals, see SIGNAL SPECIFICATION
• For information about checking and replacing the MOST cable, see FIBER OPTIC CABLE HARNESS, REPAIRING
• see OPTICAL WIRING HARNESS CHECK
• For information about location and order of control modules in the MOST network, see LOCATION OF COMPONENTS .

• Continue 

  Refer to VERIFICATION 

Checking the fault cause 

Check the fault cause as follows:

1. Ignition off
2. Disconnect the MOST connector from the CD player module (MP2)
3. Connect the MOST cable to special tool see 9512867
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
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 fault cause is then in the CD module (MP2). 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 CD player module (MP2)
• Check the MOST connection. Check for dirt, loose connections and damage
• Replace the CD player module (MP2) if no fault is found.

Click the VCT2000 symbol to read off the status of the MOST network.

Remedy as necessary.

Other information: 

• To access or replace the CD module (MP2), see MINIDISC / CD CONTROL MODULE, REPLACING
• For information about checking the power supply and ground terminal, see CHECKING THE POWER SUPPLY AND GROUND TERMINALS
• For information about signals, see SIGNAL SPECIFICATION
• For information about checking and replacing the MOST cable, see FIBER OPTIC CABLE HARNESS, REPAIRING
• see OPTICAL WIRING HARNESS CHECK
• For information about location and order of control modules in the MOST network, see LOCATION OF COMPONENTS .

• Continue 

  Refer to VERIFICATION 

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 see 9512867
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
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.

Click the VCT2000 symbol to read off the status of the MOST network.

Remedy as necessary.

Other information: 

• see PHONE MODULE (PHM), REPLACING
• see CHECKING VOLTAGE / GROUND CONNECTION
• see SIGNAL SPECIFICATION
• For information about checking and replacing the MOST cable, see FIBER OPTIC CABLE HARNESS, REPAIRING
• see OPTICAL WIRING HARNESS CHECK
• For information about location and order of control modules in the MOST network, see LOCATION OF COMPONENTS .

• Continue 

  Refer to VERIFICATION 

Checking the fault cause 

Check the fault cause as follows:

1. Ignition off
2. Disconnect the MOST connector from the MD player module (MP1)
3. Connect the MOST cable to special tool see 9512867
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
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 fault cause is then in the MD player module (MP1). 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 MD player module (MP1)
• Check the MOST connection. Check for dirt, loose connections and damage
• Replace the MD player module (MP1) if no fault is found.

Click the VCT2000 symbol to read off the status of the MOST network.

Remedy as necessary.

Other information: 

• To access / replace the MD module (MP1), see MINIDISC / CD CONTROL MODULE, REPLACING
• For information about checking the power supply and ground terminal, see CHECKING THE POWER SUPPLY AND GROUND TERMINALS
• For information about signals, see SIGNAL SPECIFICATION
• For information about checking and replacing the MOST cable, see FIBER OPTIC CABLE HARNESS, REPAIRING
• see OPTICAL WIRING HARNESS CHECK
• For information about location and order of control modules in the MOST network, see LOCATION OF COMPONENTS .

• Continue 

  Refer to VERIFICATION 

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 see 9512867
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
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.

Click the VCT2000 symbol to read off the status of the MOST network.

Remedy as necessary.

Other information: 

• To access / replace the multimedia module (MMM), see MULTIMEDIA MODULE (MMM), REPLACING
• For information about checking the power supply and ground terminal, see CHECKING THE VOLTAGE / GROUND TERMINAL (2003-2006)
• For information about signals, see SIGNAL SPECIFICATION
• For information about checking and replacing the MOST cable, see FIBER OPTIC CABLE HARNESS, REPAIRING
• see OPTICAL WIRING HARNESS CHECK
• For information about location and order of control modules in the MOST network, see LOCATION OF COMPONENTS .

• Continue 

  Refer to VERIFICATION 

• 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: 

  • To access / replace the infotainment control module (ICM), see INFOTAINMENT CONTROL MODULE (ICM), REPLACING
  • For information about checking and replacing the MOST cable, see FIBER OPTIC CABLE HARNESS, REPAIRING
  • For information about location and order of control modules in the MOST network, see LOCATION OF COMPONENTS .

• Continue 

  Refer to VERIFICATION