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

[masq]

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?

[glachhman2]

possible that one of the modules within the ring in on its way out, or the power/ground is unstable.

[masq]

I had ABR in Houston diagnose the issue, and found that a faulty MULF is the likely culprit. It's likely defective, but ABR suggested that it could be a Bluetooth pairing getting stuck in pairing mode, since my iPhone isn't fully compatible with this car. A system reset by disconnecting the battery seems to have done the trick for now, but I'll probably have to get the unit replaced if the problems persist.

[BPMSport]

We have tons of MULF's in stock if that's the issue. Good luck.

[masq]

I had the stealer replace the TCU, but it doesn't seem to be what's been causing the problem. Now, I've found that when the problem happens, I can pull fuse 14 in the glove box (15 amp) and put it back in to reset what sounds like the CD player. Once I do that, everything works normal.

Can anyone tell me exactly what fuse 14 maps to?

[masq]

bump

Does anyone have a wiring diagram that shows what fuse #14 belongs to?

[HotM3x]

I just picked up a 2009 coupe and my nav/idrive/radio/SOS is intermittently dead when I start the car. If I let it sit for a bit it starts back up again. I'm new at the BMW thing just trading my '99 996 in on it so I am unfamiliar with all of the acronyms MULF? TCU? Don't know what they stand for...help? where do I start with this problem?

[masq]

Originally Posted by HotM3x

I just picked up a 2009 coupe and my nav/idrive/radio/SOS is intermittently dead when I start the car. If I let it sit for a bit it starts back up again. I'm new at the BMW thing just trading my '99 996 in on it so I am unfamiliar with all of the acronyms MULF? TCU? Don't know what they stand for...help? where do I start with this problem?

Does it start back up by itself? Or do you have to restart the car?

Have you tried pulling fuse 15 to reset the system?