[N54problems]

Let me start off by saying I don’t know if this is the right forum to post this sorry if it’s not. I recently bought a 2009 335i e93 and it has the sos malfunction light when car starts with no radio no bmw chime no sound at all. I’ve tried diagnosing which problem it is on my last 335i all I had to do was replace the amp on this car the amp has the flashing yellow light meaning the amp is getting power so I moved on to the box on the left under the trunk that fiber optic wire has a flashing red light meaning it’s getting power I think? The box on the right I can’t get all the way out because of the trunk peice blocking but it is hot to touch and read that if that one goes out the box on the left won’t have red light so I assume the one on the right has power. I moved on to the fiber optic under the steering wheel and that one is connected to a little black peice so I cannot tell if it has a red light. I was told not to take it off the black plastic peice cause it will easily break the cable but I don’t know what other way i would be able to tell if it getting power besides taking it off the plastic peice.

The usb port in middle compartment does not work if that anything to do with this my screen will reset turn off and turn back on again every now and again don’t know what that has to do with it. Any help from someone more experienced or more knowledgeable would be greatly appreciated I ordered some of the fiber optic loop to try and fix it but idk what help those are going to do if every cable still has red light coming through. Thank you for any help

[sam9116]

SOS error? Does your car have an SOS button near the sun roof?
If you do, either replace the TCU module, bypass it with a MOST fibre optic loop, or take the connection out of the MOST junction box

Having red light is normal, not seeing red light coming out of the MOST cable would be a problem

[lordnikon]

This gives an overview of the system.

[N54problems]

Originally Posted by sam9116

SOS error? Does your car have an SOS button near the sun roof?
If you do, either replace the TCU module, bypass it with a MOST fibre optic loop, or take the connection out of the MOST junction box

Having red light is normal, not seeing red light coming out of the MOST cable would be a problem

Yes I do have the sos button I have tried plugging the fiber optic loop into the Most junction box and that did nothing. How would I bypass the tcu because it doesn’t have a fiber optic plug in that I could bypass with the loop? I have tried plugging the loop into about box in the trunk with nothing but following the red light to every source and still has red light. The no power in the usb leads me to believe my problem is the most junction box but still no sound even with bypass loop. I’m about to just take it to a dealer for them to charge me a arm and leg.

[spazzz]

Do you have a most bypass cable?
I unplugged the Telematics unit on my stepsons '09, X5 and plugged the bypass into the cable. The SOS went away and radio worked.

We got the cable from Amazon.
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

[sam9116]

Originally Posted by N54problems

Yes I do have the sos button I have tried plugging the fiber optic loop into the Most junction box and that did nothing. How would I bypass the tcu because it doesn’t have a fiber optic plug in that I could bypass with the loop? I have tried plugging the loop into about box in the trunk with nothing but following the red light to every source and still has red light. The no power in the usb leads me to believe my problem is the most junction box but still no sound even with bypass loop. I’m about to just take it to a dealer for them to charge me a arm and leg.

most bypass loops are supposed to be plugged at where your modules sits, not at the MOST junction box
your car is 2009, it's impossible to have a tcu without MOST plug, please refer to this video