# No warning tones & SOS System malfunction - broken MOST Bus ring



## masq (May 17, 2013)

Something along the MOST bus ring in my 2011 M3 seems to keep getting disconnected, breaking the loop. This causes the audio to cut out, giving me a “SOS System Malfunction” error, as well as giving the message on the iDrive screen of “No warning tones”. 

Some interesting things that I’ve seen from this issue:

- This problem comes and goes. As of late, the issues are present more so than not. Just last week, this problem was only happening maybe once a week. This tells me the amp/fuses/components itself are still functional.

- A couple weeks ago, this problem would happen every time I hit a small bump on the road. This made me think that it’s probably a loose connection somewhere, or maybe some damaged wiring?

So far, I've done a visual inspection of the following:

- The premium sound amp located in the trunk (driver side). The single MOST bus connector seems to be fine, and the red light glows when I disconnect it.

- The telematics and radio unit thing in the middle of the trunk has two of those bus connectors, and both seem to be passing red lights. If I disconnect the connector closest to the front of the car, then it causes the red light on the connector that goes towards the back of the car to turn off.

- The fiber optics connector behind the driver-side rear seat side bolster (by the seat belt) has 4 wires going in & out of them. Visually, they all seem fine and are connected firmly.

What else should I inspect to ensure that everything is connected firmly? And if it's not an issue of something being loose, what else could it be?


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## xx (Jun 2, 2013)

Do you have that connector behind your radio inside the dash? (Mine has a pair there but it's a different radio/vehicle though.)


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## masq (May 17, 2013)

I pulled the idrive screen and the AC controls earlier. Didn't see any of the fiber cables back there. I suppose I should try pulling the CD player too?


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## xx (Jun 2, 2013)

yeah/maybe. Mine was part of the big quadlock connector behind the cd/dvd player.


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## fdriller9 (Oct 19, 2006)

The SOS error is from the BMW Assist portion of the TCU module freezing. Any time a module on the MOST bus freezes, it brings the entire bus down with it. Your audio system's amp is on the MOST bus.

If you don't have a BMW Assist subscription, you can have BMW Assist coded out of your car. Bluetooth should remain active and you should no longer get the SOS errors.

Or you can replace the TCU have it coded into the car.


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## Wumpscut223 (Oct 23, 2014)

I'm having a similar issue 

http://f30.bimmerpost.com/forums/showthread.php?p=17699229#post17699229

When you unplugged the MOST connector in your amp was the ignition on or off? Was the light steady red or pulsing every second or so? My stealership wants me to buy a new amp... they are claiming spill damage.

Thanks!!


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## Bluesugar (Jan 1, 2011)

Hello all,I have a 2007 650i vert that is having these same symptons.I do not know what a MOST is!...I was just driving along and the radio would come and go(like I was turning it on and off)and it finally quit giving audio,then I noticed a "SOS malfunction" looking at me in the "heads-up"display....What should/could I do about this(not counting going to a BMW dealership,which is over an hour away and I have no extended warranty)as I am retired(electrician)and have plenty of time and not alot of monies!!...thanks in advance,..Richard


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## masq (May 17, 2013)

After many months of heartaches from the issue, I found the culprit. It ended up being a defective fuse that wasn't fitting properly. So every time I went over a bump, it would wiggle out of contact and reset the radio thus breaking the MOST ring.


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## jdauria (Oct 4, 2012)

masq said:


> After many months of heartaches from the issue, I found the culprit. It ended up being a defective fuse that wasn't fitting properly. So every time I went over a bump, it would wiggle out of contact and reset the radio thus breaking the MOST ring.


which fuse was it?


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## masq (May 17, 2013)

memory is a bit fuzzy, but I think it was fuse 14. just check all the radio fuses, which should be 14, 15, 18, 19, 27 or something like that.


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## jdauria (Oct 4, 2012)

masq said:


> memory is a bit fuzzy, but I think it was fuse 14. just check all the radio fuses, which should be 14, 15, 18, 19, 27 or something like that.


Thanks. My E70 X5 35d has no radio, sound, bluetooth or comfort access after returning from vacation. Found a MOST terminal loop in the left trunk compartment, so I need to see where that goes. I am hoping it's an easy fix like plugging the loop back in or a blown fuse. I know the amp was recently replaced so hopefully nothing major!


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## masq (May 17, 2013)

When's the last time your battery was replaced? Modern BMW's seem to do weird stuff when the battery is going bad, and I've always read inconsistent list of stuff that stops working.


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## jdauria (Oct 4, 2012)

masq said:


> When's the last time your battery was replaced? Modern BMW's seem to do weird stuff when the battery is going bad, and I've always read inconsistent list of stuff that stops working.


Still on original battery (2011), I guess I should take the voltage. I'll check where that terminal loop goes first before looking into the battery. I did just get back from a week vacation so the vehicle sat (not on a tender)


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## dalem8203 (Jun 20, 2017)

*Dale Morse 2017 X6M*

My nav screen has been constantly posting No Warning Tones and of course no sounds come from the B&O System. Today I pulled the panel on the driver's side rear and put an ice pack on the B&O Amp for 10 seconds. I started the car and all the sounds were back. After a complete inspection of the amp, I noticed none of the cooling fans were running in the amp. This is not repairable at the dealer and they ordered a new amp. There are none in North America so I Called the Factory Rep in NJ. The B & O amp must come from Germany. The dealer told me 6 weeks but the factory rep said she'd have it FedXed in about 7 days. This is not a common part as it is only in the M BMWs. Not a happy camper, that and the dealer service people looked at me like I am a moron when I told them the Amp was bad. I work on $100,000,000 Fighter jets and I happen to know quite a bit about electronics.When I took it in it was working when they gave it back it was not. So I made them bring me a shop rag with ice and held it on the amp for 10 seconds. When I re-started the vehicle it worked. They turned out being the morons and ordered the amp. That is when I called the factory rep!


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## jdauria (Oct 4, 2012)

Just wanted to provide an update - everything has been resolved now. It was the comfort access door handle the entire time...It's great to have all this technology but seriously a PITA when it comes faulty electronics. CAS door handle was shorting (getting very hot) causing the fuses to blow. Hot enough that it started to melt the door handle - mind you this was all done at the dealership and not in my possession. Dealership winds up covering the cost of the door handles (two of them), and the rest of the work to fix the issue.


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## BeMyBimmer (Oct 5, 2017)

jdauria said:


> Thanks. My E70 X5 35d has no radio, sound, bluetooth or comfort access after returning from vacation. Found a MOST terminal loop in the left trunk compartment, so I need to see where that goes. I am hoping it's an easy fix like plugging the loop back in or a blown fuse. I know the amp was recently replaced so hopefully nothing major!


I have exactly the same problem, can you tell me if you were able to fix the problem? was it a fuse. The additional issues I have are that when I try to work in the tone menu, treble, volume speed, etc., it moves a bit and jumps back to where it was.


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## jdauria (Oct 4, 2012)

BeMyBimmer said:


> I have exactly the same problem, can you tell me if you were able to fix the problem? was it a fuse. The additional issues I have are that when I try to work in the tone menu, treble, volume speed, etc., it moves a bit and jumps back to where it was.


No it was the comfort access system itself. There was a short in the door handle that threw off the entire electrical system... :thumbdwn::tsk:


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## BeMyBimmer (Oct 5, 2017)

jdauria said:


> No it was the comfort access system itself. There was a short in the door handle that threw off the entire electrical system... :thumbdwn::tsk:


 -

you mentioned the radio and the other sounds that were not working either... was that fixed too?


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