BMW MOST BUS DIAGNOSTICS AND REPAIR, E90 EXAMPLE 

Thanks so much for this info! My 2006 650 had a radio cutout/ SOS green light intermittently. The dealer wanted $2200 for a new head unit. Thanks to you I spent 1 hour and $8 on a bypass loop. It works fine again, with no unusual indications.

I have a 07 e91 wagon I just bought and was getting a sos on the dash, I watched so many other videos and not one of them mentioned the port under the dash. I looked at it and the loop there was missing. I put a most loop on and it cured the problem!! thanks a lot for this video

OMG THANK YOU SAVED ME SO MUCH TIME AND MONEY AND WAS. ABLE TO FIX PROBLEM WITH MY DONER Car!

Great video, thanks for sharing and showing the MOST diagnostics port under the drivers side. Many sources don't talk about this connection point.

Can i use the termination loop as the bypass for the satellite module? Just to diagnose before i buy the actual bypass loop

Hi! Please help!! On my 06 330, the light is on at the amp, but off at the Bluetooth thingy in trunk and off on the wire under the steering wheel… I haven’t been able to test the voltage due to not having the tool. So that means it’s the amp that needs replacement???

My radio sounds but it won't turn on by itself with the car, there is some problem with the communication to the amplifier when I scan the car, any ideas what could be wrong?

What does it mean if there is the orange light but it’s solid and NOT blinking?

I have a 2008 e90 335i. I’m trying to figure this out on mine. That little red led light won’t blink on any of my unit connections. Also my satellite is MIA. Would that be a reason why my audio isn’t working?

Question - Recently bought an 08 528i. Sos malfunction on along with aux & cd greyed out, with no sounds from the radio at all but I can hear the radio fan on & sometimes slight static from passenger side speaker. When I unplug everything I get a red light on the amp connector, plug that in then light moves to satellite, then to the telephone control module but when I check the head unit connector in my glove box I have no light from it at all? Tried bypassing each unit one by one but got nowhere. I checked all fuses & they were good. Any suggestions ?

Hi i have bmw 330d m sport 2007. I have sos malfunction light on the dash. I checked the boot theres only TCU unite. Theres no satellite unit and no amp unit in the boot. Hope you could help. Thanks

Hey my friend I don’t know if you still working with this or not but, in my case I have a328i 2011, and is working perfect but sometimes is just not turning on when the car is on. The radio can turning on in like 10 or 15 min by it self . And another thing that i see is , if my phone has the Bluetooth on never get the radio ON, I check the fiber and is blink it on

Amp blinks yellow (logic 7) all the fiber optic plugs are blinking red except for the one under the steering wheel. Radio buttons work but no sound or chimes any suggestions? Tried to bypass the sat module and other one even though the fiber optic connections were blinking red and still nothing.

Question - what if you don't have the satellite tuner? Would you still use the jumper? I have intermittent radio on/off, the SOS light comes on/off, and the bluetooth stopped working (gives a high screeching sound when the phone is connected until the phone drops again). Would the telephone module need to be replaced if I don't have a satellite tuner?

What if yellow light is not blinking ? But still same issue is present?

On my BMW 328i 2010 the amplifier is not on the trunk, could it be inside the dash?

Is this all done while the radio is on?

Hi, I have a problem when I checked all fuses, optic fiber has no lost connection, and amp steady yellow. Still no sound. I have Logic 7 amp and most module. Any ideas what else I can do?

After so many hours researching my SOS malfunction and stereo problems I found this video to be unbelievably helpful!! Thank for for this and also for taking the time to make a Diagram!! Great vid. Many thanks!!

I have a clicking or popping sound coming from my speakers. It doesn't matter if the radio is on or not, the car can even be off and still popping sound coming from the speakers. The only way to make it stop is to unplug the and amp. I have replaced the amp but the amp is good. So I was watching your video about the most bus and when i checked my fiber optic cable going to the amp, it isn't red. What could that be? Sorry i'm not very versed in electrical stuff at all! Lol

I reviewed a few other video about this topic. Your explanation of the the fiber network was excellent. I was able to isolate my problem. it was the sat radio module. Thanks you save me $$$

I have tried everything. I have bypassed or tried to bypass all of the components. I still get an sos issue

So what if your speakers just pop but sound come in just popping and cracking

What if you have no power to the headunit/amp/etc... YES the fuses have been checked...

Thank you!!!! I was able to stop the most annoying tapping/popping, occasional buzzing because the SAT unit died. I am so eternally grateful!!!

no power at all to my 16 pin bus, and radio obviously has no power either

What if you did put the loop in and you still don’t have the blinking light under the dash?

Others have already said it but THANK YOU. It's beyond me why this seems to be one of the only videos explaining the system in simple / understandable way. Saved me hours of headache in minutes. You have my gratitude

what if my fiber optic that goes in my radio unit is removed?

Hi when i disconnect plug from satellite unit and plug it back in the radio comes on until i hit a bump in road. Then it goes off. I bought the loop today assuming the satellite unit has something broken inside.

Can I pay you to diagnose my car? Dealer said the amp needed to be replaced... do you live in the NYC area?

thanks for saving me money!!!

Hi i changed my MULF with MULF2 on my E90 (MULF has bluetooth issues) after i set MULF2 it work perfect for two months now when i trying to connect my phone with bluetooth on bmw professional radio it stuck on "bluetooth devices pairable..." and cannot connect with my mobile phone

I have an Audi issue with my 07 E90. I ran the diagnostic per your video. However, the red fiber optic has no break and it goes out and back to the head unit without breaks. But I still have no sound!! I don’t have navigation. What would be the reason for no sound? Door/seatbelt chime is super low and it comes from the dash. Please help!!!

I have a 2008 E93 with the "SOS call system malfunction" with no radio or sounds for the key, lights, seatbelt alarms. I have red blinking fiber lights at the telephone mod and to the Satellite mod, no blinking lights at the amplifier or under the dash. Tried bypassing the Satellite with jumper, this didn't help. The Christmas lights sequence does match what you diagramed. Can someone please advise?

I followed all the connectors on my 2006 330i and they all light up but I’m still not getting any sound from my radio or door chimes. I checked all my fuses and they’re all good. I’m not sure what to check anymore.

What if your stereo doesn’t work, checked all fuses, took stereo out and it works in another car, no power to the radio or sound from it. Could a faulty mulf module/amplifier in the boot, cause this problem?

Can you use the termination plug as a bypass loop to test the potential fix?

Hi! My radio stopped working and the SOS light came on on my BMW 335i E93. In my case the AMP was broken so I connected a loop. After this the SOS-signal turned off but still NO sound from the radio. Any idea what this could be??

i have no lights on the optical to the amp. can anyone help me please

Mines stop at the cd/dvd unit in my 6 series what do I do

do any one know the part number for that lil tool I have 2 from BMW but they don't fit

Mine shows all lights on? What could it be

This video fixed my 2006 e90 330i pre-lci that hasn’t had sound for about a year. I was inches away from buying a new amp but thanks to this man i didn’t. I simply bought the part listed in the link in the description, plugged it in less than 10min and heard the classic BMW ping. What a guy. I appreciate it!!

Thanks man

Would the steering wheel connection be on the square on the steering colum for an F30 3 series?

I have a ‘06 330xi (e90) and have this same exact issue, the light at my tcu is blinking (I don’t have a sat tuner), but the cable under my dash has no light. I disconnected the cable at my tcu and connected the fiber optic loop, but the light is still off under the dash. Any idea what else it could be? So basically I only have the amp, tcu and block off connection under the dash. Cable at the amp and tcu are blinking, but the block off is dead. Fiber optic loop on tcu cable doesn’t fix issue and block off connection is still dead/no light.

THANK YOU, SO MUCH, SIR! This is the most helpful, most straight forward BMW DIY video on RU-vid!

So my e92 sound just went out. I can see that the fiber optic cable lights up when I unplug it from the LOGIC7 Amp. However when i plug the FIBER OPTIC back in, the Amp's internal troublshooting LED is RED, not Orange. Does that mean the AMP is bad, or is the head unit bad thus not providing signal to the amp? I am not sure what the RED LED means, its not orange so I know something isn't working. I think maybe the issue is the head unit, but I cant say for sure, bc when I Loop the TCU unit, the Fiber Optic Loop for the Termination Loop, blinks fine. Please any help would be appreciated. I've been at this for a week now, the Head unit, powers on, ejects CDs just fine. I have also checked all my radio fuses, I have reset the radio by holding both EJECT and POWER. nothing is bringing sound back not even the sound when you open the door with the key and headlight on.

What if everysingle one of my lights are lit up but i still have no audio and theres no sos light too

How to connect extra cooling on that thing on the left side in front of stop light

Wer is the fuse located for the amp my amp haves a red light thers no Amber light can you help please basically I have no sound I had sound yesterday we had down paw last nyt and I noticed water near the amp whats got into the car after 9 hours of rain I need to no why red light and not Amber

I have a 2007 750i and my subwoofers don’t work. My side speakers work but not my subs under my seat. It turned on randomly for like 30 minutes but that was it

If the amp is bad would the red light to the telephone module work?

Why does it on mines it has a white light

My car has signal everywhere and I have 1 looped connected signal goes all the way back to the front termination loop. And my idrive works perfect but I have no radio sound or door chimes. Need help!!!

Awesome video, I went through this diagnosis as much as I could, there is no light in my amp, I’m guessing that means the amp or the line is bad. However, the radio does not even power on. I have a non idrive so just the regular radio. Nothing in the screen, I checked the connection with a volt meter and got the proper 12V. Also there is no satellite module in the back of mine, just the phone module. I’m assuming that some cars don’t come with it as I don’t even see the loose wires that would indicate that there had been one installed. How would you bypass without the satellite module. I get the sos and caution sign on the dash upon startup. I drive a 2008 BMW 335i E92 with the logic7 setup.

i have no blinking light to the amp

I’ve got no red light on any connection

what if my head unit is not giving any signal to the AMP? do i need to replace the CCC unit?

One rat got inside of my 2008 335 e92 and the rat ate my harness from the glove box fuse box, you have not idea I had to remove the glove box and fix all the harness, days trying to find and doing bypass to the amplifier, till I found your video, the connector on the driver side was disconnected 🤦🏽‍♂️ I bought this car as a project and the previous owner or mechanic leave it disconnected, thank you so much sir!

my amo doesn’t have the light does that mean that my amp is bad?

The problem I'm having is that when I start my car, sometimes the volume works and sometimes it doesn't. After I installed my aftermarket Android head unit, I didn't get any sound and the SOS light popped up. I bought a MOST fiber optic interface for the head unit which converts the fiber optic into 2 RCA inputs to the back of the head unit. This provides sound but only sometimes. If I don't hear sound, I have to restart my car a few times and then the sound comes on. Any advice on how to fix this?

What if the radio doesn’t turn on??

I have problem with SOS failure and BT not working. I connected second TCU unit but still not working. In ISTA i have 3 errors : 1. VIDEO 2. CD Charger 3. Telephone. How i can try to fix it?

I replaced my logic 7 with a used one and still doesn't work, does it have to be decoded? Thanks

I have no base but otherwise the stereo works fine. Checked all the red lights and they all work. I don’t have the satellite radio. And it seems the phone is first from the head unit, followed by the amp then end. That’s what the red lights showed me at least. Amp has solid yellow light. What else should I check?

Hello my amp light blinking my telephone magual blinking also but my satellite tuner is not but then I put the bypass wire on the telephone magual then the satellite tuner blinks still have no sound

the fiber optic that plugs into the amp isnt red what could be the problem head unit i suppose 0:38

Why no light coming from my amps fiber optic wire to the telephone module?

So what if my first wire (the only in the beginning of the video) has no red light

I have a video i need to show u. Can u help me please!!! Its been more than a year without radio. I believe in mine its the ccc, cd changer, satellite, l7, and bt the last one.

I believe my 2010 e93 has the sat integrated with the head unit. So I see the red light at the connection to the amp. And the next module in the trunk after the amp is the TCU and the fiber optic going to the TCU doesn’t have the red light. So does that mean my amp is bad?

I bought a used 2006 330i and the dealer I called said it was prepped for the satellite tuner when it was originally sold but when I went to diagnose why I didn’t have sound the module wasn’t there connected to the TCU it was completely absent, is the SAT module necessary for the Audio to come out? Before I purchase a SAT module I’d like to know. Is it possible to make my car that’s coded for it work without it? Ps my amp has a yellow light, all fiber optic connections are red, and the fiber optic loop I connected to the amp and the TCU didn’t bring my sound back.

I have the red light all the way to the one under the dash but my sound system still won’t work. Is there a fuse I can try? Or is this something else

This is the first time I’ve dealt with this, I got the SOS randomly after hitting a bump I suppose. I checked every optical loop in this video and none of them are flashing red or any color at all. I tried the bypass loop on all of them and nothing. Idrive screen is black, no music, radio, door chimes etc, if anyone knows what I should do or look at or if I’m doing something wrong please help. (2008 335i w logic 7)

Only my head unit blinks red. What does this mean?

I have a 330i e90. My speakers had a large 100db screeching noise, 15 min later it stopped. I have 0 audio on anything (Inc aux) would that be my logic 7 Amp that's busted? I also don't have a SOS sign showing up... so I'm confused on what to do.

Hello, Asking if you may know, if any of my fiber optic cable at the trunk is broken/cut, let’s say from the telephone module, will I still be able to use the bypass kit for the other fiber line to run the system normally without the module with the broken/cut fiber optic line?

I have the MOST bypass loop and attempted to diagnose this but am coming to a blank. Amp has yellow light that blinks, confirming amp is functional. Checking all connectors from amp to Bluetooth to sat radio all have the red light. Using the bypass loop or having the connector plugged to the sat radio module, the final termination under the dash has no red light. Any ideas?

Thank you for your video, I have a yellow flashing led on my Amp, but the amp is not outputting a infa red signal to the next MOST module. If I remove input infa red input to the Amp at the processing board then the amp starts pushing out a output signal on the output infa red. If I loop out my Amp on the MOST bus all over MOST modules work?

I have red light blinking even under the steering. Is the existing loop not working?

Hey youtubers! Hope you can help me with my issue: After leaking I got no sound in my '07 e93 (no radio/cd/aux and no warning sounds at all). After couple sunny days a full sound came back and then on the next day the right side of speakers is not working (now only left side of speakers working). Guys any solution?

What if the radio wont wake up from its sleep mode? Does it have anything to do with the fiber optic? Its intermittent.. Sometimes radio wakes up sometimes it takes time

So i bypassed the tcu and the red light is now flashing at the wire under the dash but still sos error and the amp is flashing yellow light, do you know what the problem could be? The only thing after the under dash wire is the radio, could the radio be bad?

My e90 2011, showed that SOS light this morning on my dashboard when I inserted the key in the ignition. When I tried to push to start the brake felt hard and my car wouldn’t start. I kept trying it till finally it started. Can the SOS be a reason to why that happened?

" we call it christmaslight " and in fact it is Token Ring. you CAN build the loops yourself - but you need special tools and the connectors. that was no diagnostic it was a lesson how to tell other ones how can they got money. PERIOD

I have no light coming from the setallite tuner, or the one inside under the driver side. The amp an the one to the right of the setallite unit both have red lights?! Help!

Forgot to say, my radio works there's just a popping/clicking sound coming from the speakers and the only way to stop it is to unplug the amplifier.

What do you do if there is no red light to the amplifier. I should add that I had the complete interior out of the car including the center consul. After putting it back together I have no sound at all and there is no light at the amp.

Can I send my logic 7 to you?

my rear speakers dont work on my coupe any ideas everything else works just no bass

My brothers BMW is missing the termination loop on the last wire shown on the drivers side. Can you use a jumper loop on it? Or does it have to be the one shown in this video? (the termination loop)

what is the correct term for the loop? whats the correct term to tell the sales associate?

My connections show all white, then the first one starts blinking red for like 5 seconds then goes back to white. What could it be?

What do I do if I’m missing my satellite radio?

Hi my light is only red not orange can anyone explain ????

So which ever one isn't blinking is the broken part?

Thanks so much for such a detailed video! My subs and mids have not been playing for a while now and instead of just spending $1000 or more to replace it, I am going to use this video as an example troubleshooting method. Because I do have power at the head unit and highs, should I approach this differently? Any clues or assistance will be certainly helpful.

I did all that and still nothing no sound