In this post we will be describing how to diagnose MOST bus failure in any BMW, AUDI, PORSCHE, ROLLS ROYCE, RANGE ROVER HSE, BENTLEY with MOST fiber optic bus. every car has different configuration, but principle is still the same!
So in 2000 they introduced newer multimedia bus, called MOST, IT IS VERY NICE AND FAST NETWORK, SO THERE IS ENOUGH SPEED TO CONTROL EVERY MULTIMEDIA DEVICE AND THEY ELIMINATED LOTS OF COPPER WIRES IN THE CAR. NOW SOUND IS FULLY DIGITAL AND CLEANEST (BC NO SIGNAL LOSS ON THE WIRES), SO IT IS A GOOD THING, BUT ITS MORE COMPLEX AND NOT VERY RELIABLE.
So to start you need to understand that all MOST (multimedia) modules in the car work in the closed loop, which means if any device in the loop fails-none will be working.MOST bus primary signal (optical red light signal) is generated inside of the main computer, which is your main screen CID (control display or CID in E65 car only, other BMW have main computer incorporated into head unit or CCC/CIC/NBT etc), then it travels through all MOST network devices (ask unit, amp, navi, fm tuner, phone etc. depending on how many options you have) and comes back into main head unit. Basically all units connected in the loop- one unit fails=broken network! Once you understand this principle, you can easily find broken unit or network interruption, don’t forget dealer will charge up to 500-1000$++ for such a serious job! You don’t believe me? go and try, then you will understand how priceless with post is.
Your E65 E66 or Rolls Royce phantom ( yes don’t be surprised it is the same exact car as your 760li btw) car has MOST bus failure if:
-cannot hear any sounds or music
-cannot see tracks playing on the display
-fm stations not available
-navi isn’t functioning
For other BMW like e60/e90/e70/e89/f01 and others MOST BUS FAILURE symptoms are little different because primary head unit has 4-5 modules (SVS, ask unit, MOST GATEWAY, NAVI, Radio tuner) combined and therefore everything will work except for those secondary modules:
-amplifier no sound and you see mute icon on the radio or screen
-TCUM or telephone module
-SAT NAV receiver
Here is the MOST DEVICES order diagram , but this is only valid for basic order and only for pre 2006 cars, you might have way more devices in the network, so you have to figure it out yourself by looping eac modules and draw a diagram of the modules.
Here is a quick video showing how to find a bad unit in real time:
FOR 2006-2008 E65 E66 cars basic order will look like this:
MMIGT(screen)>>CDC>>AVT(if you have it)>>TEL>>SAT(hd RADIO)>>L7>>SVS>>NAVI>>ASK>>OOPS(GLOVE BOX MOST LOOP)>>MMIGT
FOR E60 E90 E63 E89 E90 E92 E93 and so on:
HEAD UNIT CCC/CIC/NBT>>L7AMP>>SAT>>TCU>>MULF>>HEAD UNIT
On these cars in most cases i see sat and amplifier unit failure very often, telephone module goes bad too but not that often.CCC navi units have a high rate failure, but the good thing once you replace it, you replace 5 modules at once, so its more reliable and much easier to find a faulty unit because you only have 2 or 3 modules to diagnose and all of them located in the trunk. We also offer CCC or CIC repair service
So to find out the faulty unit you either need to see a dealer (but even dealer makes mistakes), but here is an easy solution if you don’t have anything, and if you do it right it always works:
You need basically to find out where the most signal gets lost, after what device you don’t see the red light. In other words you will be checking the red light after every device in the network, and the one which is not sending the red light signal is your FAULTY MOST UNIT. OOPS is the last diagnostic connection located in the glove box and it has lollipop attached and it has to be looped there, some people think it is a spare jumper, but its not, without this jumper you will interrupt the network!
HOW TO BYPASS NON WORKING MODULE??? EASY! GET THIS P/N FROM ANY BMW DEALER 61136917541, YOU CAN GET IT ONLINE FROM ECS TUNNING ECS TUNNING FIBRE OPTIC JUMPER. YOU HAVE TO REMOVE INNER PART WITH SOME FLAT SCREWDRIVER OR A KNIFE, YOU CAN ALSO USE ZIP TIE IF YOU PLAN TO KEEP THE JUMPER BYPASSED, IRT WON’T STAY WITHOUT ZIP TIE.
most common MOST devices failure (descending from most common to less):
-SAT SIRIUS unit always goes bad, we will offer repair of this unit soon
–TCU TELEPHONE BLUETOOTH MODULE RECENTLY WE SEE TONS OF THEM FAILING!
-Logic7 amp AMP
-ask cd unit ASK
-navigation NAVI
-fm tuner
-CD itself main screen CID
-cd changer CDC
-SVS (gets flooded with hydraulic fluid from trunk opener cylinder, if you see sticky fluid on the NAVI, SVS- replace asap)
other modules. depending what you have in your car
Always check if you have red light in the glove box, disconnect that jumper and check for the light, if you found and bypassed bad unit correctly you should see the red light in the glovebox and then you can install the jumper and everything should start working. I know it sound complicated but once you understood how it works it is kind of very easy.
BUT PLEASE DO NOT BLINDLY BYPASS EVERY MODULE, LIKE LOTS OF PEOPLE DO, YOU MIGHT FIND THE PROBLEM, BUT ITS NOT EFFICIENT AND SOMETIMES YOU CANNOT DIAGNOSE IT RIGHT. ALSO MAKE SURE EVERY MODULE HAS 12v POWER. BASICALLY EVERY MODULE NEEDS FIBER OPTIC SIGNAL AND 12V POWER ATTACHED TO FUNCTION.TO WAKE UP MOST NETWORK IT IS ENOUGH TO OPEN/CLOSE THE DOOR, YOU DON’T HAVE TO START THE CAR, THE THING IS MOST GATEWAY WILL GO TO SLEEP AFTER 10 MINUTES IF NETWORK IS BROKEN AND TO WAKE IT UP YOU NEED TO OPEN/CLOSE ANY DOOR OR TURN ON THE RADIO. 
THAT’S about it, IF YOU FOUND THE BAD MODULE YOU JUST SAVED 300-400$ AND TIME. REMEMBER LOTS BMW SHOPS STILL CANNOT DIAGNOSE IT RIGHT AND ALWAYS POINT TO ASK UNIT OR AMPLIFIER, “BECAUSE THERE IS NO SOUND”, WHICH IS NOT ALWAYS TRUE, I WOULD SAY IN 50% ITS NOT CORRECT EVEN FROM OFFICIAL DEALERS. WHY THEY MADE IT SO COMPLICATED AND NOT RELIABLE?? WELL THIS A FUTURE OF CARS AND TECHNOLOGY, YOU ARE THE ONE WHO ASKED TO HAVE ALL THESE TOYS IN THE CAR, SO YOU EITHER LEARN IT OR HAVE YOUR WALLET READY TO GET SKINNIER, OR BUY HONDA/TOYOTA….
Hello, I have a 2007 Audi Q7 I have no sound and my mmi screen is black, mmi s=comes on for a second and turns back off. I Replaced the amp. still not working what canoe the problem?
you nned to fix your mmi most likely, contact us using email we can help
I have a 2008 e70 x5, have followed your diagram and method , I have red light at all most connectors even one under glove compartment. When I use cd changer it works fine , sound etc great. I have no radio (although stations are shown) no pdc, chimes , nav sound or cd in dash also no sound but reads the CD and tracks fine. Any idea ?
amp is bad, we can help, email us
hi i have a 2002 745i i have no sound in both my front doors and subs and rear doors are making a static noise when i turn it up some. subs sound like they want to come on but cut in and out. only clear sound i get is from the center dash speaker. i have checked the loop to everything and it all lights up. pulled out the tape player unit and i have light there to. can you please tell me what could be my problem i would be so gratefull
amp is bad and ask unit, we can fix them both, email if interested
There is no sound in my 2011 BMW X6. There is no blinking light on the amplifier, I have the optic loop and have yet to find the module with the issue. I think the issue may be with the module either before or after the amp but I don’t know where they are located. Can you tell me where the SVS is located?
no svs in your car, svs is for older cars. email us if interested we can help you out
What’s up dude. My sound system in my 08 750i was only playing out of the passenger door and I could hear bass throughout. Read a thread, unplugged the loop in the glovebox and plugged it back up and everything was AWESOME for a few weeks. Now the sound has moved to the driver door with bass throughout. My navigation, screen front and back, work fine. The changer in the front and the DVD player in the trunk dont register in my entertainment options. Is it the loop? Your help will be greatly appreciated.
SOUNDS LIKE AMP NEEDS REPAIR
I have a 2011 328 XDrive. A year ago my bluetooth became unstable – it would connect to the pone but instantly drop the connection – unusable. A couple months ago all the sounds (radio, CD, AUX, chimes etc) stopped working, too. GPS Navigation works. SOS Call function does not work. Also, at random times the display shows some kind of electrical problem – shops speculate that there is a loose end in the wiring.
I looked in the trunk, and my car only has the Amplifier and Combox (bluetooth) there – no satellite unit, even though I had satellite before the breakdown. There is blinking red light in the cable going into the Amplifier, but no light in the cable going to the Combox. Do you have any advice? Thanks in advance.
SOUNDS LIKE COMBOX FAILED
Have a bmw 08 e90 m3 the audio works when the car turns on , sometimes it only comes from the back. but it always works from the back no matter what. when driving the sound turns moves from left to right and noting in the front when hitting pot holes. what could the issue be? amplifier?
amp problem
Hi,
Need help. I have E60, 2005 with HiFi amp(not 7 logic, a small one). I try to install AUX and didn’t disconnect the battery. Aux was not working, so I removed it. After I check my sound and there was no bass anymore. Woofers under me were not working but other speakers rear and front was working fine but sound like crap without bass. Amp is also good I just order a new one. Could be that the signal is not coming to the amp. Could it be M-ASK fault or Sirius satellite?
bass signal comes from ask unit, and then goes through the small amp in the back, just check if it has 12V in the back, if yes most likely its the ask unit
2011 bmw 750 li no sound at all, BMW house said amp is bad, is there any other thing i can check to verify this? Sometimes it could be sometime simple and they want $3000 for a new and installed amp. If this is blown i will remove it and send to you once I find the location of it.
in the trunk: behind left side panel
Hello. I have e93 335i 2007. Ive followed your way to diagnose why no sound at all on my car. I see all red lights are seen from logic7, tcu and bluetooth ( all three in trunk) but no red lights from head unit most fiber connector. What can cause the problem?
is there yellow led steady on in the amplifier? sounds like a bad amp, but you need to make sure there is red light near sterring wheel termination loop point (SMALL SQUARE PLASTIC). if you see the light everywhere it means there is output from head unit.