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 AM/FM tuner module (AFM) and traffic message module (TMC).
If the vehicle is equipped with an Integrated Audio Module (IAM), its fuse must be removed as well.
3. Wait at least three minutes.
4. Ignition on
5. Reinstall the fuse(s) within 25 seconds.
Note! If more than one fuse is removed, ensure that the fuse is reinstalled in its original location.
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.
Note that the AM/FM tuner module (AFM) and traffic message module (TMC) do not normally take part in a ring break diagnosis if the fuse is removed. This means that a break position is displaced two steps rearwards in the MOST network.
On a fully equipped vehicle where the break position is 5, the fault could be due to:
- Multimedia module (MMM).
- The fiber optic cable between the multimedia module (MMM) and AM/FM tuner module (AFM).
- AM/FM tuner module (AFM).
- The fiber optic cable between the AM/FM tuner module (AFM) and traffic message module (TMC).
- Traffic message module (TMC).
- The fiber optic cable between the traffic message module (TMC) and the audio control module (AUD).
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.
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.
Click on the VCT2000 symbol to obtain a MOST network status reading.
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 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 diagnosis detects a break in communication on the MOST network the result will be a break position.
- If there is no fault in the MOST network the result will be OK.
- 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 diagnosis always counts backwards irrespective of the purpose and number of control modules fitted in the vehicle. To determine the break position, check the control modules fitted in the vehicle against the list. Then count backwards, starting from the predetermined order. The number of control modules may vary between 2 and 9.
Two examples are given in the following:
- The first break position corresponds to 0. This indicates that the break is located in the media player module (MPM) or the cable between it and the infotainment module (ICM)
- If the position is 1, go one step back in the chain and the break will then be located in the phone module (PHM) or the cable between it and the media player module (MPM). The break may also be due to a damaged optical connector in the media player module (MPM), which will then be unable to correctly interpret the incoming signal from the phone module (PHM).
Note! The phone module (PHM) is not standard and if not fitted, break position 1 would then correspond to the subwoofer module (SUB).
Select an alternative which includes the control module that is to be checked.
Alternative 1:
Media player module (MPM)
Phone module (PHM)
Subwoofer module (SUB)
Global positioning system module (GPS)
Integrated audio module (IAM)
Alternative 2:
Audio module (AUD)
Traffic message module (TMC)
AM/FM tuner module (AFM)
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
- Component locations Component Location, Infotainment
The media player module (MPM) can be replaced by the integrated audio module (IAM).
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. Media player module (MPM)
2. Phone module (PHM)
3. Subwoofer module (SUB)
4. Global positioning system module (GPS)
5. Integrated audio module (IAM)
Select the control module.
1 - Checking cable and component
2 - Checking cable and component PHM
3 - Checking cable and component SUB
4 - Checking cable and component GPS
5 - Checking cable and component IAM
-------------------------------------------------
Checking cable and component
Select the control module to check according to the list.
1. Audio module (AUD)
2. Traffic message module (TMC)
3. AM/FM tuner module (AFM)
4. Multimedia module (MMM)
5. Infotainment control module (ICM)
Select the control module.
1 - Checking cable and component AUD
2 - Checking cable and component TMC
3 - Checking cable and component AFM
4 - Checking cable and component
5 - Checking cable and component
-------------------------------------------------
Checking cable and component
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 media player module (MPM).
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.
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 media player module (MPM). 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 media player module (MPM) power supply and ground connection.
- Inspect the MOST connection for dirt, loose contacts and damage.
- If no fault can be found, change the media player module (MPM).
Remedy as necessary.
Click on the VCT2000 symbol to obtain a MOST network status reading.
Other information
- Media Player Module (MPM), replacement Media Player Module (MPM), Replacement
- Checking the supply voltage/ground terminal Component Tests and General Diagnostics
- Signal specification Pinout Values and Diagnostic Parameters
- Diagnostic Instructions - Fibre Optic Cable Diagnostic Instructions - Fibre Optic Cable
- Fiber optic cable harness, repairing Fiber Optic Cable Harness, Repairing
- For information on the location and arrangement of MOST control modules, see Component locations Component Location, Infotainment.
Continue - Verification
-------------------------------------------------
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.
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).
Click on the VCT2000 symbol to obtain a MOST network status reading.
Remedy as necessary.
Other information
- Phone Module (PHM) Phone Module (PHM)
- Checking the supply voltage/ground terminal Component Tests and General Diagnostics
- Signal specification Pinout Values and Diagnostic Parameters
- Fiber optic cable harness, repairing Fiber Optic Cable Harness, Repairing
- Diagnostic Instructions - Fibre Optic Cable Diagnostic Instructions - Fibre Optic Cable
- For information on the location and arrangement of MOST control modules, see Component locations Component Location, Infotainment.
Continue - Verification
-------------------------------------------------