[ctuna]

shine a light in one end of the fiber and see it come out the other end.
Though the Fibers themselves almost never fail .
(unless they crushed or cut) there could be a loose connection at one end though.)
Each module should have one side emitting red light while unplugged
and powered up.Logic 7
Wiggle connections while it's working to find intermittent connections( or fiber at junction points )
https://www.e90post.com/forums/showthread.php?t=1056432
https://www.bavlogic.com/?p=3729
https://www.bavlogic.com/?tag=loop
http://www.bmwlogicseven.com/?p=3837
http://www.bmwgm5.com/
https://www.e90post.com/forums/showt...5#post24455335
http://www.e90post.com/forums/attach...2&d=1260829447
http://www.google.fr/url?sa=t&rct=j&...slMu2A&cad=rjt
https://www.bmwgm5.com/Logic7_E90_91_92_93.htm
http://www.bimmerfest.com/forums/sho...d.php?t=982666

http://www.e90post.com/forums/attach...1&d=1209780605
Most
http://www.e90post.com/forums/showthread.php?t=727663
http://www.e90post.com/forums/showthread.php?t=347222
https://www.google.com/search?q=BMW+...VCkMqy2aCK09M:
http://www.1addicts.com/forums/showt...php?p=19256760
https://www.teacremotes.com/bmwgm5/
Diagnostic Manuals Inpa/Ista D
https://bimmerprofs.com/diagnostics-inpa-part-1/
https://www.google.com/url?sa=t&rct=...7x8H3pN8h1fMuF
https://carmod.ru/files/icom/istad_en.pdf
https://www.e90post.com/forums/showthread.php?t=1681573
https://www.bimmerforums.com/forum/s...-P-actually-do
primary links
https://www.bimmerfest.com/forums/at...9&d=1539905743
https://www.e90post.com/forums/showthread.php?t=1681573
https://www.bimmerfest.com/forums/at...1&d=1590283589
https://www.nathansbmwworkshop.com/b...or-dean-videos

Before you do any work on these cars of any kind always be sure
you have a good battery with good battery voltage and good alternator voltage.

BMW standard tools and Ista/d or plus is always recommended.

If you have HI FI there is no Most connection to that amp it would have nothing to do
with your problem.
Try re seating the connectors at the Combox at least the ones on the major connectors.