Media oriented systems transport (MOST) diagnosis

Overview 

The basic guidelines are covered in the description and operation section, such as not attempting to repair fibre optic cables, but additional precautions include:

• Do not touch the exposed ends of the optical fibres (grease from skin can contaminate the fibre)
• Whenever the fibre optic cable is disconnected, cover the connectors to prevent dust contamination
• Do not expose the fibre optic cable to heat
• Do not bend the fibre optic cable through less than a 25 mm (one inch) radius
• Do not use laser pens to test the fibre optic cable's ability to pass light

  There is a dedicated tester to use with the MOST network modules and fibre optic harness to assist with diagnosis and to test the fibre optic cable's ability to pass light

MOST tester 

Before connecting the tester to the network, turn on the unit and check that the red power on  indicator is illuminated.

If not, the battery should be replaced before using the tester.

2+0 Self-test 

1. Set the connector selector switch to 2+0.
2. Select beep  or LED  on the tester, depending on your choice of indicator.
3. Turn the tester on and check the operation of the power indicator.
4. Using the 2+0 loop-back lead from the kit, push it into the 2+0 connector housing in the tester until it clicks into place.
5. Press the red test  button in the center of the tester.
6. Depending on your choice in step 2, the tester will give either an audible tone or a green light.
   • If the tester continues to give a tone or light after the test button is released this does not indicate a fault, only that there is a signal feed-back within the tester which will stop when the loop-back lead is removed.

   2+4 Self-test 

   Carry out the self-test in the same way as for 2+0, but using the 2+4 loop-back lead and select 2+4 on the connector selector switch.

   Vehicle diagnosis 

   CAUTION: Make sure the tester is not connected to the MOST network when either switching the tester on or switching between 2+0 and 2+4, as the tester emits a brief pulse of light which could introduce a fault into the network.
7. Use the approved diagnostic system or a scan tool to retrieve any DTCs.
8. Set the connector selector switch to 2+0  .
9. Disconnect the intermediate fibre optic cable connector and connect the male half to the tester connector at the top of the unit using the adaptor in the kit.
10. Turn the tester on and check the operation of the power indicator.
11. Set the LED/beep  selector to LED  .
12. Turn the ignition switch to the ON  position.
13. If the green LED is active, a signal has been received indicating that the first half of the optical ring is functioning.
14. If the green LED is NOT  active, no signal has been received indicating that the first half of the optical ring is NOT  functioning.
    • A ring break code should be set as a result of this. Use the approved diagnostic system to trace the fault and clear the code.