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….
My stereo starts sounding a little staticky when volume is turned up. Also my driver side woofer under seat isn’t working at all. My driver door speaker doesn’t work either. Sometimes it may appear out of the blue then go off. Per your description of faults, it sounds like it is the ASK? Do you agree?
both units need repair: ask unit+amlpifier
I have a 650i that has no sounds at all. I see the changer, nav radio stations, music on harddrive(?) and can connect bluetooth. My dealer said it was the tcu but I bypassed it with the loop. I see the red light going to the tcu.
In the MOST diagram are you speculating that it is the ASK since that is the only thing after the TCU (if TCU=Tel).
most likely the amp is the problem, you didnt read it right, E65 system differs from e60/e63/e64
Okay so I have an e60 545i 2004. There is no sound at all coming through my speakers. How this happened was that my mechanic replaced my alternator and did not tighten up the clamps on the battery and while driving hit a pot hole and the clamp came off which made my car shut off. I figured out that the clamp was off so put it back on and turned the car back on. The sound started going in and out immediately. Did this for a few minutes and then just cut off completely. I bought a used amp. Plugged it in and no difference. What do you think is the issue??
sounds like amplifier problem, but could be other unts a swell, you need to torubleshhot with my article
I troubleshoot my system and the red light is missing in the ask unit, communication module and the GPS. What could be the problem?
2004 745Li
cannot be 3 modules, you didnt do it right.
you need to find out which unt causes failure and why no red light in the last endpoint in the glovrebox
I have the same problem with my car 2003 745i.
All lights on the modules are working except the one at the glove compartment, What do you think the problem is?
Thanks!
GLOVE BOX IS THE LAST POINT, SO IF YOU SEE THE LIGHT BEFORE ASK UNIT, IT MEANS ASK UNIT IS BAD
What device sends the red signal to the navigation unit? When i unplugged the harness that’s where i don’t see a red light. The other harnesses have red light
Did you read the post with the diagram?
Logic7>> Svs >>sends signal to navi, so check before and after logic 7. If car is before 2006 it is most likely the amp
Hi
I have a more complicated l7 idrive issue, maybe this is one of the spin offs of common MOST BUS device failure or other equipment in the Multimedia network.
After a minor collision i started having lights come on weird messages. I lost the beep for pdc, initial key beep, and the voice command works but no sound from anything.
the whole system will keep on cycling on and off consistently every few seconds whether car is movingor stationary.
The car was sitting in the body shop for 40 days, but i installed the correct AGM battery 7/14 and registered it witht the software and usb obd cable. I have looked through the inpa software or ncs expert but couldnt find anything logical that would help out.
I also have driver and pass airbag faults and light is permanently on. The airbag light wasnt reset by the shop to see if it would come back or a mere jolt from the impact.
The car was drivable after just popped tire and damadged rim. no fluids leaked, no check engine.
If i try to turn the audio system on (all options are still available if i can carry out the functions i need (like setting the3 clock) before the whole system resets and turns off and screen flickers and turn back on, then ill have music for a few seconds (cd works, changer works, nav hasnt worked in over 6 years without effecting anything else. I have adjustment in the l7 levels,radio stati8ons, everything. My TPMS hasnt worked in 4 years.
I also had an aftermarket amp and 10″ sub installed or added to the system (some piggybacking on the wiring and that was working without a single hitch for over 6 months. Now i noticed the aftermarket amp is not getting a remote turn on signal from where it was tapped into the factory wires right above the battery and on/off switch for power.
I just figured out why my previous battery didnt last, my nav cd reader in the trunk has the ON and CD IN light always on, but i could never eject the cd, and nav screen says insert cd.
Am i dealing with multimple possible failures? I do not have the fiber optic jumper eliminator pieces to eliminate a failing module. I have no desire to have navigation im fine without that old archcaiac setup.
One last thing the idrive knob sometimes loses its feedback tension and it lags like on a computer when you type and it appears a second or two later sometimes too. when the things stays on for the few seconds i have full sound except my aftermarket sub connected to aftermarket amp. nothing is greyed out in the idrive.
If you have a few minutes and can give me some tips with the symptoms above.
It is a 1/2003 build 03 745i, 95k, bought as a CPO with 20k miles on it.
Which bmw software is best to test modules and reset them? INPA? ive read through your threads btw. thank you for your efforts!
Not having music daily is now starting to effect me wanting to drive the thing. I had no idea i was addicted to audio!
is it possible to just run an aftermarket independent sound system without touching any existing pieces (l7 amp, speakrs, sub, ask, changer etc). Im sure it will labor intensive running new to the doors for some MBquart 6.5″ seperates with an existing 4 channel amp and just have 2 channels for the satelittes in the front doors and the other 2 channels bridged for the 10″ sub i l aready have in the trunk?
only pro lem where do you mount an aftermarket deck. I know on this car there no real usable glovebox. Is that just foolish and crazy? The only wires i need to use from the factory is power ground, switched lead.
Thanks,
JSPEC E65
jspec1@gmail.com
510-444-4669
nothing serious… you need Logic7 amp fixed or replaced. send me your units and ill diagnose them and rebuild as well
My subs on my BMW 745i 2002 re not working but when I tested the two cables powering the woofer the be power both of them now what cud be the problem
You need your amp fixed to get subs working again
My subs re not working but when I tested the two cables powering the woofer the be power both of them now what cud be the problem
I see that it’s $240 to repair l7. How much to repair ask and how long does it take? I’m in Atlanta Ga
Same price. 1-2 days
hello,
both my front passenger speakers are crackling, is there any possibility that those speakers are defect (is it possible)? all other speakers are working fine on my logic7 .
speakers are fine, your amp is bad causing it.
check on the bottom of the page, so we can help you out
Ok replaced ask unit bit on getting sound mids& highs on passenger side only oh & both subs work! Any idea?
most likely your new ask unit is no good. did you install new one or used??
if ask unit is ok, you should get front doors and rear deck working at least. speakers almost never go bad