[sonick]

Yet another day, yet another electronic gremlin in a BMW.

This is on my BMW professional head unit, I think hi-fi system (not L7) but it has amp, door tweeters, Bluetooth, aux, optical.

Symptoms/troubleshooting findings so far:
- no audio from radio, aux, CD, etc.
- no door chimes
- no SOS malfunction error code
- MOST optical loop is intact (the diagnostic port under driver footwell is lit)
- battery voltage 11.6v in ACC, 14.5v engine on
- THE KICKER: when I turn up the head unit volume to max, I can hear audio from the radio and door chimes very faintly, which leads me to believe the audio signal is intact.

I am leaning towards an issue of the amplifier since I can hear the correct sounds when I crank up the head unit. Also because it affects the door chime as well, which would not be the case (I think) if it was a head unit issue.

Another possibility I've read is that the battery is low and so it's going into a power conservation mode, but I don't know how to confirm this. I have noticed in the past year I would get battery warnings when I would leave the car on too long without the engine running, but have not experienced it since this sound issue.

Anybody know how I could diagnose the amp? Or if anybody has come across this problem?

[ctuna]

You need to replace that battery regardless of the sound problem.
Try a long slow charge on the battery and see if you can get it above
12.4 and see if it fixes the problem.

Charge the battery from under the hood at the charge points.

A healthy new battery will measure 12.6 to 13 when fully charged.

electical e90 pdf
http://www.google.com/url?sa=t&rct=j...,d.cGU&cad=rja
http://www.google.com/url?sa=t&rct=j...85464276,d.cGU
http://www.google.com/url?sa=t&rct=j...85464276,d.cGU

[TboneS54]

I'm having the same exact issue.

My battery is fine though.

Already put in another, working amp, to no avail.

I'm not even getting any hiss or noise whatsoever no matter the volume.

[sonick]

I put the battery on a 2 amp trickle charger both in the car and outside the car over 2 days, peaked at 12.1v on cold.

However I did gamble on an amp from the wreckers and fortunately it fixed things!

The fact that I hear faint noise when the HU was cranked up really tipped me off. If you hear no noise whatsoever then it's likely not the amp.

Will look to getting the battery replaced, but happy that I figured out the audio issues.

[TboneS54]

Lucky fukker that didn't work for me

I have a question though, why did you mention MOST optical loop? Isn't that only on L7 cars? I haven't found anything optical in my system and I have hifi (mid range system).

[ctuna]

The Most Bus attaches to bluetooth , phone and sat modules in US Cars regardless
of which sound system you have.

In some of the last e90's this was sometimes integrated into the Head Unit.
Some Euro cars don's have a Most BUS but almost all US Cars do.

[TboneS54]

Oh ok, do you know where I may find it to inspect. Someone told me that the audio in these cars can get wonky if even one module in the loop is down.

[ctuna]

BMW stereo types
http://www.e90post.com/forums/showthread.php?t=352586
http://www.e90post.com/forums/attach...2&d=1266451970
http://www.e90post.com/forums/attach...2&d=1260829447
http://www.e90post.com/forums/showthread.php?t=138949
http://www.e90post.com/forums/attach...1&d=1209780865
http://bmwcoders.com/forum/3-er-8/bm...1-e92-e93-291/
http://technicpnp.com/menuDiagrams/d...e90_92_93.html
http://www.musicarnw.com/page-2/
http://www.e90post.com/forums/attach...3&d=1169133185
http://www.e90post.com/forums/attach...1&d=1209780605
http://www.e90post.com/forums/showthread.php?t=641323
http://www.e90post.com/forums/attach...4&d=1278871872
http://www.e90post.com/forums/showthread.php?t=343673
https://www.bimmerfest.com/threads/e...n-752.1275694/
The following thread's will tell you more about the most bus
I know you said you don't have logic 7 but the procedures still apply.
Logic 7
https://www.e90post.com/forums/showthread.php?t=1056432
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

[TboneS54]

Are you sure there's a MOST system in a car with the hifi system (not L7)?

I've been through the vehicle and haven't found anything optical or that looks like anything in those videos and links.

AFAIK, only L7 is fiber optic ?

[ctuna]

Did you look under the trunk floor behind the back passenger seat.
Take a picture and post it.

http://www.e90post.com/forums/attach...2&d=1260829447

page 36 of the above document.

And I suppose the car you are talking about is not the E46 you have in your handle since you
are on the E90 stereo forum.
And not a coup or convertible because the modules will be in slightly different positions in those
and I don't know where but still in the Trunk.

Yes I have Hi Fi in Mine and it had a TCU before I replaced it,
with one of these (in the following link in mine)
its and e90 though.

https://www.e90post.com/forums/showthread.php?t=1499808

If you have something other than and e9x all bets are off . If you have a 4 cylinder in the
could be and f series.

[TboneS54]

The only electronic equipment in the trunk is the amp in the driver side quarter panel floor. This is a 2012 128i. Tweeters in the sails, 8" subs under seats, 4" mids in doors/rear panel. Hifi, professional h/u. I'm quite positive there's no fiber optics.

But OP said something about MOST loop being intact. He doesn't have L7, so I don't know how that's possible. But I asked because my audio isn't working, and the only thing left I can think of, is something software based or some module. H/u works, usb works, tried 2 amps, wiring is fine, speakers are fine.

I'm grasping at straws at this point.

[ctuna]

Bottom line pull out head unit or idrive and see there is an optic line plugged
in to the Radio Harness.

You can't have a SOS error without a TCU , Mulf 2 hi or Combox.

Amp has 12 volts inject signals some noise should come out..
One guy on here bought a used car only to find there where no speakers in the locations
that weren't playing.

This is not rocket science.

[TboneS54]

There isn't. No SOS error either. Just no sound.

Don't give me that shitty tone of "it's not rocket science."

If it's so easy, why don't you give me the right answer? You've never read or come across an e6/8/9x generation car with hifi system where everything works fine, good battery, but no sound or chimes?