Part 1
Faulty signal
951 2867 MOST instrumentation 951 2867 MOST Instrumentation
Checking the wiring and component
The infotainment module (IAM) has detected a communication break in the MOST network.
The MOST network is a fiber-optic ring network in which all control modules connected to it must be supplied with current and grounded to ensure proper functioning of the infotainment system. Should a control module for any reason be unable to process (receive or transmit) the MOST signals or if there is a break in the fiber-optic cable, the infotainment module (ICM) will shut down all functionality.
Communication on the fiber-optic network is one-way. The MOST network control module receives the light signals, amplifies them and then retransmits them. 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 will have been registered on an earlier occasion but is no longer present. Intermittent faults may either be due to interference on starting the MOST network or to an intermittent power supply and/or grounding fault in a control module forming part of the network. The fault will be assessed from case to case. If the fault recurs, carry out fault tracing as for a permanent fault.
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 it will be necessary to run a ring break diagnosis to locate the break.
Continue - Break checking
-------------------------------------------------
Break checking
Ring break diagnosis
A ring break diagnosis should be performed to determine where the fault has occurred.
Get the MOST system to perform a complete ring break diagnosis, as follows:
1. Turn ignition off and remove key.
2. Remove the fuse for the infotainment relay. For information on fuses, see the wiring diagram.
3. Wait at least three minutes.
4. Ignition on
5. Reinstall the fuse(s) within 25 seconds.
6. Wait at least 30 seconds after ignition on before taking a break position reading.
Other information
- For information on fuses, see the wiring diagram.
Continue - Obtaining a break position reading
-------------------------------------------------
Checking cable and component
If the result of the ring break diagnosis is POOR it indicates that the infotainment module (ICM) receives signals on the MOST network but cannot decode them because the light strength is too weak or the signals are distorted.
If the result of the ring break diagnosis is OK it indicates that the fault is intermittent.
Fault tracing with ring break diagnosis presupposes that the fault is permanent or active while the test is running, i.e. when the system is powered up after a period without power.
Hint: If diagnostic trouble code ICM-DC01 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
- Unplug 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 MOST network communication is in working order. Do this by obtaining a status reading of the MOST locked parameter for at least 30 seconds. This parameter shows whether the MOST network is closed and communication possible. Click on the VCT2000 symbol to obtain a MOST network status reading.
If MOST network communication is stable when a control module is disconnected, check the power supply and ground connection of the control module for an intermittent fault. If no fault is found, try changing individual components.
Continue - Verification
-------------------------------------------------
Obtaining a break position reading
- Ignition on
Obtaining a reading of the ring break diagnosis result
Obtain a reading of the ring break diagnosis result by clicking on the VCT2000 symbol. The script also presents a list of all control modules connected to the MOST network.
The following results can be obtained from a ring break diagnosis:
- If the fault occurs while the ring break diagnosis is running the result will be presented in the form of a break position.
- If the fault does not occur while the ring break diagnosis is running the result will be OK. In such case continue by selecting alternative 3 below.
- If the infotainment module (ICM) receives signals on the MOST network but cannot decode them because they are distorted or the light strength is too weak, the result will be POOR.
Determining the break position
The break position is counted backwards from the infotainment module (ICM) in the MOST network.
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.
Two examples are given in the following:
- First open circuit position is indicated by 4. This means that the open-circuit is in the Remote Digital Audio Receiver (RDAR) or in the cable between the Remote Digital Audio Receiver (RDAR) and the Audio module (AUD).
- First open circuit position is indicated by 2. This means that the open-circuit is in the Phone module (PHM), or in the cable between the Phone module (PHM) and the Integrated Audio Module (IAM). The open-circuit may be caused by the optical connector in the Integrated Audio Module (IAM) being damaged. This means that the Integrated Audio Module (IAM) does not interpret the incoming signal from the Phone module (PHM) correctly.
Select an alternative which includes the control module that is to be checked.
Alternative 1:
Accessory USB unit (AUU).
Phone module (PHM)
Integrated audio module (IAM)
Bluetooth phone module (BPM).
Alternative 2:
Audio module (AUD)
Remote Digital Audio Receiver (RDAR).
Multimedia module (MMM)
Infotainment control module (ICM)
Alternative 3:
The ring break diagnosis result shows that the MOST network is OK.
The ring break diagnosis result 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
-------------------------------------------------
Checking cable and component
Select the control module to check according to the list.
1. Accessory USB unit (AUU).
2. Phone module (PHM)
3. Bluetooth phone module (BPM).
4. Integrated audio module (IAM).
Select the control module.
1 - Checking lead and Accessory USB unit (AUU)
2 - Checking cable and component PHM
3 - Checking cables and components, Bluetooth phone module (BPM)
4 - Checking cables and components, Integrated Audio Module (IAM)
-------------------------------------------------
Checking cable and component
Select the control module to check according to the list.
1. Audio Control Module (AUD).
2. Remote Digital Audio Receiver (RDAR).
3. Multimedia module (MMM).
4. Infotainment Control Module (ICM).
Select the control module.
1 - Checking cable and component AUD
2 - Checking cables and components, Remote Digital Audio Receiver (RDAR)
3 - Checking cable and component
4 - Checking cable and component
-------------------------------------------------
Checking cable and component PHM
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 cause of the fault
Check the cause of the fault as follows:
1. Ignition off
2. Unplug 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 MOST network communication is in working order. Do this by obtaining a status reading of the MOST locked parameter for at least 30 seconds. This parameter shows whether the MOST network is closed and communication possible. Click on the VCT2000 symbol to obtain a MOST network status reading.
7. If the parameter shows that the MOST network is not closed, check the receiving control module in the same way as described above.
If menu text is displayed, communication on the MOST network is OK. The cause of the fault then lies in the phone module (PHM). Continue fault tracing by checking the component.
If menu text is not displayed, communication on the MOST network is not OK. The cause of the fault then lies in the next control module. Continue fault tracing by checking the fiber-optic cable.
Checking the cable
- Inspect the MOST connection for dirt, loose contacts and damage.
- If no fault can be found in the MOST connection, change the MOST cable.
Checking the component
- Check the phone module (PHM) power supply and ground connection.
- Inspect the MOST connection for dirt, loose contacts and damage.
- If no fault can be found, change the phone module (PHM).
Remedy as necessary.
Other information
- Phone Module (PHM) Phone Module (PHM)
- Checking the supply voltage/ground terminal Checking Voltage/Ground Terminal, Phone Module (PHM)
- Signal specification Signal Specification, Phone Module (PHM)
- Fiber optic cable harness, repairing Fiber Optic Cable Harness, Repairing
- Diagnostic Instructions - Fiber Optic Cable Diagnostic Instructions - Fiber Optic Cable
- Location of components Component Location, Infotainment
Continue - Verification
-------------------------------------------------
Checking cable and component 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 cause of the fault
Check the cause of the fault as follows:
1. Ignition off
2. Unplug 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 MOST network communication is in working order. Do this by obtaining a status reading of the MOST locked parameter for at least 30 seconds. This parameter shows whether the MOST network is closed and communication possible. Click on the VCT2000 symbol to obtain a MOST network status reading.
7. If the parameter shows that the MOST network is not closed, check the receiving control module in the same way as described above.
If menu text is displayed, communication on the MOST network is OK. The cause of the fault then lies in the audio module (AUD). Continue fault tracing by checking the component.
If menu text is not displayed, communication on the MOST network is not OK. The cause of the fault then lies in the next control module. Continue fault tracing by checking the fiber-optic cable.
Checking the cable
- Inspect the MOST connection for dirt, loose contacts and damage.
- If no fault can be found in the MOST connection, change the MOST cable.
Checking the component
- Check the audio module (AUD) power supply and ground connection.
- Inspect the MOST connection for dirt, loose contacts and damage.
- If no fault can be found, change the audio module (AUD).
Remedy as necessary.