User manual

VCDS – Optical Bus Diagnostics - Section 29-A
The [Optical Bus Diagnostics] function found in the Applications Screen is used on
models with a MOST bus to narrow down the location of a break in the network. Many
control modules will be completely inaccessible via conventional diagnostics if there's a
break in the MOST bus.
The above example shows a 4F Audi A6 with a break in the MOST bus. In this case, it's
clear that the modules are all electrically OK, but the Optical bus is broken between the
Sound System module and the Voice Control module.
You may change the Diagnostic Type from "Standard" to "3dB Attenuation" if your results
are not conclusive. The attenuation means all modules are sending with less output
(initiated by the MOST master), but the individual MOST participating control modules can
attenuate individually to check if individual modules are responsible for problems.
VW/Audi sells a handy loop of fiber (part number 4E0 973 802 ) that can be used in place
of each of the components in the system. This can be used to check whether a component
is responsible for breaking the loop.
Click on [Start] to begin checking the controllers on the bus.
[Copy] will copy the results to Windows Clipboard. Once you have pressed the Copy
Codes button, you may paste the results into the application of your choice, such as MS
Word or Notepad.
[Save] will save a plain-text report to your PC, typically in this directory: C:\Ross-
Tech\VCDS\Logs
Use [Done, Go Back] to return to the Applications screen.