SOS and Radio inop

[El Versace]

Whenever I drive the car for a long period of time, let's say like 2+ hours, my radio goes off and my SOS mil comes on and the radio won't work for a long while, then it'll come back on and it won't be able to be as loud as it was. Usually I know when the radio will go out because the volume will go low, and I won't be able to raise it back up. Whenever I turn off the car and let it sit for a minute, then start it up, everything goes back to normal. Can I get some help with this issue

[asbrr]

Sounds like you might have a head unit or amplifier that's about to go - or basically one of the units on the MOST bus is about to go.

The amp, head unit, bluetooth, satellite radio, and a couple of other modules are connected via a Fibre optic network called the "MOST bus". When one of these components has an issue, the light doesn't pass through that component and the entire "chain" goes down and typically the SOS warning comes on.

Do a google on "SOS error bmw" or similar and you'll see tons of Youtube videos and forum posts on this issue. It could be a number of things and you need to eliminate each module one at a time to see which one is causing the problem. There are probably diagnostic tools to help you do this, in my case my headunit was completely dead and it was fairly obvious, I bought a used one and swapped it, all back to normal.

[El Versace]

Originally Posted by asbrr

Sounds like you might have a head unit or amplifier that's about to go - or basically one of the units on the MOST bus is about to go.

The amp, head unit, bluetooth, satellite radio, and a couple of other modules are connected via a Fibre optic network called the "MOST bus". When one of these components has an issue, the light doesn't pass through that component and the entire "chain" goes down and typically the SOS warning comes on.

Do a google on "SOS error bmw" or similar and you'll see tons of Youtube videos and forum posts on this issue. It could be a number of things and you need to eliminate each module one at a time to see which one is causing the problem. There are probably diagnostic tools to help you do this, in my case my headunit was completely dead and it was fairly obvious, I bought a used one and swapped it, all back to normal.

How wouldnI go about testing the network? And for the headunit, would I test to see if there is anhigh resistance? I have a DMM but what else would I need?

[asbrr]

Originally Posted by El Versace

How wouldnI go about testing the network? And for the headunit, would I test to see if there is anhigh resistance? I have a DMM but what else would I need?

For the fibre optic side, there are small devices called "MOST bus Loop connector" or similar. Google those and what you would do is disconnect each component and put in the loop from the farthest to the nearest (there is an order they are connected in), one by one. Tht way you will find out where the break is...however in your case since it's intermittent (ie when the car has been running for a long time), this is going to be difficult.

I'm sorry I don't have much more to give you on this....it's going to take you some digging and search, or someone else that can chime in to assist...

[El Versace]

Originally Posted by asbrr

For the fibre optic side, there are small devices called "MOST bus Loop connector" or similar. Google those and what you would do is disconnect each component and put in the loop from the farthest to the nearest (there is an order they are connected in), one by one. Tht way you will find out where the break is...however in your case since it's intermittent (ie when the car has been running for a long time), this is going to be difficult.

I'm sorry I don't have much more to give you on this....it's going to take you some digging and search, or someone else that can chime in to assist...

I'll search one up and see where the modules are, I'm hoping it's the head unit. Today while driving home, the radio just went dead for a quick minute, then came back on like nothing happened.