BimmerFest BMW Forum banner

No Sound / SOS Error Still Stuck After Troubleshooting / Optic Loop

901 Views 18 Replies 3 Participants Last post by  ctuna
2009 335 Convertible e93 / Logic 7. (looks like I posted in wrong forum originally)

Started with loud hissing and popping sounds and I lost all sound including radio, cd, door chimes, etc. Received some kind of no audio sounds error message on the nav screen header. It evolved to the SOS error. I tried all of the stuff I could find in forums including the Optical loop off amazon. Interesting thing is all of the optical plugs showed the blinking red light (solid for a few seconds then a blink and back to solid). I was expecting one of the modules to be dark with no red light but that was not the case. I did find some water in the trunk that was toughing the amp. Not much but touching the bottom of the unit. The amp had a light green / yellow led light on (can't remember but think it was blinking). Also, I did check the optical connection under the driver dash and it too was blinking red so I put the connecter back on it like I found it. Didn't check amp fuse as I can't find a diagram saying which fuse it is and also I read that the amp will have a red LED light if it isn't getting power.

Any thoughts on what to check next? Read some random mentions of ground wire to amp maybe being an issue some times? Could I be missing a component in the loop that I should be checking? I tried some old forum posts that had links to enter your VIN so you could see what components the car has but the links are no longer working so I couldn't check it. I found the amp in the back driver side trunk, and the TCU on the middle right trunk up near the back seat. To the left of the TCU there is an empty space for I'm guessing the bluetooth but my car doesn't have that (or didn't when I bought it used years ago). Appreciate any help, would love to have the sound going again...
1 - 19 of 19 Posts
The first description with loud hissing and popping sounds usually means the amp has gone bad.
And water on the amp is the most common problem.
If any module on the Most Loop breaks they all look bad.
Could be water has attacked the other modules to .
If you put a most jumper in the amp location and the SOS light goes
out it would isolate the problem to the amp or could mean more modules
are bad.
The obvious thing is to verify the amp first.
I would stop looking elsewhere till I could verify the amp.

Logic 7 E92 Logic 7 Coding How to Troubleshoot MOST bus or how to find the faulty MOST unit ON ANY BMW, AUDI, PORSCHE, VW, MERCEDES BENZ and other cars with OPTICAL FIBRE OPTIC MOST network | BAVLOGIC, LLC LOOP | BAVLOGIC, LLC BMW E90, E92, E60, E63, E64, E61 LOGIC7 AMPLIFIER DIAGNOSTICS&REPAIR | BMW LOGIC7 BMW General Module 5 (GMV, ZKE V) SOS error, No radio - Need verification of problem BMW Logic 7 Amplifier E90 E91 E92 E93 BMW MOST BUS DIAGNOSTICS AND REPAIR, E90 EXAMPLE - YouTube Sound Car Communication Computer-M-ASK & TOP HIFI AMPLIFIER INSTALLED DSC 0633 - YouTube Wiring Diagram-l L7.jpg (JPEG Image, 600 × 724 pixels) - Scaled (77%) Most MOST Bus Fiber optic question Anyone know what is this "optical connector" under driver's side? BMW most bus junction - Google Search DIY: Individual "M" Audio/Enhanced Premium Sound (Logic 7) Retrofit BMW General Module 5 (GMV, ZKE V) Diagnostic Manuals Inpa/Ista D Diagnostics with INPA. Part 1. | | ISTA - User's Manual - istad_en.pdf Software - Help yourself What can ISTA-P actually do? primary links Software - Help yourself INPA Tutorial Quickstart.pdf BMW Doctor Dean Videos | Nathan's BMW Workshop
See less See more
Appreciate the reply and went through the links you sent. Checked fuse and it was okay. I did try the optiloop / most jumper at all of the different connection points but still now sound (they all had the red light with occassional blink when I pulled them--but plugged the jumper in anyway with no luck). Will pull the amp and look for signs of trouble as you suggest. Will also verify the led light on the amp and see if there are any trouble code hints. One other observation--I seem to be going back and forth between the SOS error and the "no audible noises" (or whatever the exact wording is). Sometimes I get one error...sometimes I get the other.
tonnes of stuff like this on ytube.
If you put the jumper in the amp location and the SOS light goes out unless you have a bad TCU or Mulf or any other module that's bad usually Sat in US car it means the amp is bad and you have completed the Most Loop.
If any link in the Most Loop is broken nothing works . SOS light is usually the indicator for that.
The SOS is out without having the jumper involved at all. There is however the "no warning tones" message on the nav screen (which is how this whole thing started...and then at some point the SOS message came and went). Does the "no warning tones" indicate the same thing as the SOS light in terms of troubleshooting? I've watched most every YT video and read tons and tons of posts but remain puzzled as the punchline to all of the videos and posts seems to be "find out where you lose the red light from the optics, plug in the jumper, and things will work / you know what module to replace. Since all of my red lights are working, this hasn't been a huge help for diagnosing what is wrong. Sounds like you are saying I can still get the red light (optical) past the amp even if it is bad? Amp needs to come out either way as a closer inspection will likely reveal there is damage as you predicted. Just trying to understand why I get the red optical light everywhere in the circuit if the amp is bad.
See less See more
Ok do you understand what a minimum system is in trouble shooting?
If you remove or jumper out all modules on the Most Bus besides the AMP you are down to two things
The AMP and the head unit.


Scroll down to the amp led description in the above
where it says

So basically you should get steady yellow LED at the amp, which will indicate the network is working, bypass not working modules and if amp is good you will get sound back to your car!
Very helpful, thank you. Well, you said I should get a steady yellow LED at the amp and I did. Unfortunately it sounds like that means the amp is bad right? I was a bit confused by the Bavlogic link you sent me as the picture with the yellow LED says "Steady yellow means network working and amp is functioning ok.". This is different from above the picture where it says "steady yellow but no sound or bad sound--amp is bad". And last, the third reference in that link says "steady yellow means its getting input fiber optic signal from the head unit (CCC or CIC) and output signal travels to head....but rarely it also could be some software glitch with CCC, when you don't get sound with working amp. Try CCC reset."
Did some digging and looks like I have a CIC on my 2009 e93 not a CCC. I did the 30 second push the volume knob down and it did reboot it. Nothing changed. Still no sound of any kind, still have the "no warning tones" message, no sign of the SOS message. I disconnected the amp afterwards and tested for 12v at the connector "plug". 12 volts were there. Bad amp?
See less See more
There are two parts to the amp the Logic Board and the actual amp board.

Opened up my L7 amp -what should i look for?
Will give this an in depth read tomorrow and dive in. Quick question in the mean time...I've read posts from other folks who had bad amps from water in the trunk like I did. I started pulling mine apart (one end is fighting me and I don't want to force it...will read up on how to get it apart)--and can see some corrosion on the non plug end where the water had accumulated in my trunk. Some folks claim to have soaked their amps in denatured alcohol, various electrical sprays, etc. and had luck with it fixing their amp. No clue if they just through a hail mary and got lucky or knew what they were doing. Any thoughts on giving this a dance given what can be viewed in the picture? Otherwise, will give the link you just sent a good read tomorrow and see what I can learn. Again--much thanks for all of your help.

Passive circuit component Circuit component Electronic instrument Hardware programmer Computer hardware
See less See more
Don't have logic 7 it's worth a try with anything that has been dunked . You can get used logic 7 amps on ebay for a few hundred buck's . I would use the high end 99 percent alcohol meant for electronics. If you can find a big enough ultrasonic cleaner I would try that to .
Got it all the way opened up (we won't talk about the fact that I missed two screws on the other end that were holding it in place...I was tired) and sprayed it with Deoxit D5 and gently scrubbed with a soft toothbrush. Seemed to really clean up the corrosion and supposedly leaves a desirable protective layer. Put things back together and plugged it back in to the car. No amber light of any kind. No similar red light either. There is however a very faint red light that was solid. I saw the note about a faint red light deep in the amp but sounds like that should be a blinking light not solid. I'm back to getting the SOS message (and the no warning tones message too). The red optic light going to the amp is still solid like before (no change there). Almost acts like the amp isn't getting / accepting power now. I did confirm 12v at the plug harness that goes to the amp. I'm about out of runway on this one. I read the link you sent me about what to look for once you open the amp up and it's above my pay grade. Couple quick shot in the dark questions: 1. Can the two black wires that go from the plug pins that go almost all the way to the other end be easily unplugged by pulling on them? Wondering if it would be worth taking them off if so and spraying them with Deoxit? Or perhaps test for 12v there if those are power wires? 2. The white grease (heat sink thermal grease?) on the top of the rectangular components...I didn't add more when I put it back together but didn't wipe off any of the old either. Assuming this isn't the problem but throwing it out there. Welcome to other thoughts as well of course. If after this it's feeling like a dead end, sounds like I'll need to either roll the dice on eBay if I can find one or try sending it in for repair. Picture of the cleaned up unit is below.

Circuit component Passive circuit component Hardware programmer Urban design Computer hardware
See less See more
I think that the two larger black wires are light pipe wires for the fiber optics. So don't spray these with Dexoist but I doubt that would hurt them. I'm wondering if the module where these teminate on the circuit board are still sending light?

Your oxidation and water ingress were definitely the culprits here. But what was shorted out or damaged is beyond scope for me. Good luck!
Thanks Mike. Ctuna--I just went out and tried plugging it back in in the dark and it was easier to see the faint red LED. It looks like it is indeed blinking (about 2-3 seconds solid and then 1 second blink). I confirmed I'm still getting red blinking light at the fiber optic plug that goes into the amp--so that should eliminate the possibility of #3 (no fiber optic input getting into the amp from the head unit) in the LED troubleshooting link you sent me. So that would leave #1 (amp is bad) or #2 (no power getting to the amp). What Mike said about the 2 black wires being optic makes perfect sense after thinking about it and I see in the picture I took that there are some other colored wires that go from the end with the plug down into something on the board. I'll pop the amp back open and gently inspect those wires / what they plug into and report back with what I learn.
I mean the first thing you said was the amp got wet how much are you going flog this.
Not hard. As I mentioned in my last post I'm out of runway on this one. Seemed odd to lose the solid yellow light and add the SOS error again after getting the corrosion off the board. Felt like I went backwards so wanted to make sure I wasn't missing something simple. Tried a couple things last night and no luck. Found a 65129170386 on eBay. Mine is a 65129181743 which looks like it should be compatible...hopefully.
This site has a list of all the part no's and compatibilty by year and model number.
Looks like it should be compatible. Will report back with the results after it arrives.
  • Like
Reactions: 1
She's alive! 150 bucks for a used logic7 amp on eBay. Guy shipped it fast and I plugged it in, saw solid LED light on amp, turned on car...heard chime!!! sound from radio. Turned up volume knob...full sound. Back to enjoying the lovely sound from the upgraded Bavsound speakrs I did a few years back.

Thanks a ton Ctuna for your help. Saved some money and learned a few things in the process.

All the best!
  • Like
Reactions: 1
The first symtoms where the wet amp failure. Anybody reading this thread should note that.
This is such a common problem there is a class action lawsuit on the 5 series board against BMW for this.
1 - 19 of 19 Posts