[imstimpy]

My wife's 2008 328i is producing intermittent, albeit frequent) audible popping coming from the speakers. It occurs on wakeup, as well as with or without the head unit on in both CD and FM. It is accompanied by a disabled SOS warning and no more bluetooth, satellite radio, nor AUX/USB input. This appears to be a MOST optical network failure and I cannot find the cause.

Troubleshooting:
* I've connected the car to an Autologic tool and cannot communicate with any MOST modules besides the gateway. Codes stored are:
FC E18D - Network wake-up unsuccessful
FC E190 - Ring fault diagnosis run
* I've pulled any fuse in the glovebox that seems relevant and only 14 or 15 stop the popping (both un-power the head unit).
* I have fully disconnected (unplugged both power and MOST connector) on the TCU, BT, and SAT to no effect. I did notice the popping sound is accompanied by the MOST optical flickering.
* The popping ceases when I disconnect the Professional headunit.
* I swapped the headunit with one from my 2010 M3 and the popping persisted.
* I have attempted to trace all MOST connections but I cannot find the MOST network junction. A single connection comes from the head unit and passes into the driver footwell, alongside the MOST loop connector. In the trunk there are four MOST line pairs, one for the Logic7 amp (not used and disabled), one for the SAT, one for the BT, and one for the TCU. The junction appears to be somewhere behind the driver's side and forward of the trunk.
* The car has a Hi-Fi amp (not on MOST network) and disconnecting it disables the sound. I need to double check if the MOST network continues to reset.
* I concluded the headunit is the source for the MOST optical signal (ASK/CCC/CD in the diagrams), de-pinned the MOST connector, and noted the MOST optical flickers at the back of the headunit.

At this point I'm going to reprogram all the modules but I'm skeptical this will have any effect. Following that I will likely de-pin the headunit, pin by pin. My current hypothesis is there is a system external to the headunit that is producing unclean power or signal that powers the MOST network.

I would love to hear additional ideas on where to go next besides the dealership.

Thanks,
-Jon

MOST References:
Sos Malfunction: http://www.e90post.com/forums/showpo...1&postcount=14
MOST Bus Diagnosis: http://www.bmwmotorsports.org/BMW_docs/mostbus.pdf
Resource- MOST bus fault patterns: http://www.bimmerfest.com/forums/sho...d.php?t=300965
E90 Entertainment and Communication: http://www.rcollins.org/m3/TIS/08_E9...munication.pdf
Stereo Crackling: http://5series.net/forums/e60-discus...ing-593/page6/

[ctuna]

Battery power and alternator voltage for noise.
If you have Hi Fi and Pro radio that connection is analog.
Isolate the modules that are on the most bus by using
a most bus jumper or bypassing them at the Most junction
under the US driver passenger side under the bolster near
the front of the rear wheel well.
If you disconnect the most bus at the radio the radio should still
play if you have hi fi actually I think you unplug the most bus anywhere
as it breaks the but . What does the radio sound like with the most bus
disconnected ?

Sounds like the TCU or Mulf module from the the first errors described.
Could be the satellite module to.
I doubt its a programming issue.

[imstimpy]

The alternator is not in the equation since this issue happens with the engine running or not. The battery and intelligent battery sensor were replaced less than a year ago (properly recoded as well). I don't think my voltmeter updates fast enough to monitor voltage for stability, but I have access to a scope at work.

All MOST modules that I can find, besides the headunit, have been unplugged from the MOST bus and disconnected from the vehicle. The only thing left connected to the MOST bus is the headunit and the junction but I can easily pull the headunit from the MOST again. A MOST jumper would accomplish nothing since the headunit cannot be bypassed.

While the popping appears to originate at the headunit, I don't think it is the source. It appears to be receiving the instability, not creating it. Bad power, ground, or wakeup could be causing the headunit to cycle its outputs (MOST bus included), thus creating the popping noise and disabling the MOST bus.

[rambca]

I have experienced similar issues with popping sound and loss of Bluetooth but recently I regained Bluetooth functionality except for calling (I can stream audio). Playing audio from external devices (Bluetooth, USB) occasionally results in the popping sound but the radio seems unaffected.

This leads me to believe the issue is TCU related (TCU module is located in the trunk).

You said you disconnected all the MOST modules... Did you disconnect the TCU? As far as I'm aware, disconnecting the TCU prevents the head unit from powering on.

Are the fiber optic connections solid at the back of the head unit? I know I had to fix mine after my head unit stopped powering on altogether. Now I'm just missing bluetooth calling.

Let me know if you find anything. I know first-hand how frustrating it is.

Best of luck.

[imstimpy]

In a non Logic7 system (Basic or HiFi), bypassing the MOST system entirely still allows the amp and headunit to power on and produce audio. I can go so far as to affirm that the headunit will power up with only 12V BAT and GND. The MOST connection is entirely disconnected from the headunit in my case. I ran out of time building a bed of nails, so to speak, to power on the headunit with clean power and ground and produce audio on a single channel to check for the issue.

I just had a realization that nullifies most of my testing. I just disconnected the MOST connector from the headunit in my M3 (different car entirely) and the same audible popping occurs at roughly 3 second intervals. The location and sound is different, but pretty close. I think the continual optical cycling is a discovery/wakeup mode in the MOST network and not a sign of a bad signal going to the headunit. I'm going to see if I can swap modules between the cars, while keeping the network linked, to see if the issue is a module or a break in the network itself. My M3 doesn't have the same modules as the 328, but it has most of them.

[rambca]

Interesting. In my car (base stereo), the TCU unit needs to be plugged in for my head unit to power on. I also found that my head unit required a good fiber optic connection to power on. If I disconnected the fiber optic connector from the head unit, it would no longer power on.

[ctuna]

Find another amp and swap it in.
Seems logical unless you can find something on
a scope . You may need a sampling scope to catch
this event.

[rambca]

No pun intended right ctuna?

Personally I'm going to try another TCU unit in my car and see if it fixes things.

[TexTide]

Did you ever fix this problem? I'm having the same issue in my 08 328 sedan.

[TexTide]

Well I replaced my battery and the noise is still there, SOS waring still pops up.

[zspear]

I have this EXACT same issue to the letter. Were you ever able to fix this?

[ctuna]

If you have lost all sound the order of common failures is.
Water on the amp
A failed Most bus module.

Always be sure you have a strong battery and a good alternator
voltage before starting to repair/troubleshoot problems on these cars.
IBS system can turn stuff off with a low battery.

[zspear]

Thanks for the reply ctuna! - However, I haven't lost all sound. Sound works. I have the popping noise, disabled SOS, AUX not working situation that was described earlier in this post. A little elusive. It seems the way to diagnose this is to jump individual components on the MOST network.

When I pulled the headunit out, I am seeing a blinking red light that is in perfectly in sync when the speakers pop.

As of now, my fiber optic knowledge and diagnostic ability is about a 1 out of 10. So I need to do some searching on how to do that and go from there I think. I was just hoping that the originator of this thread found a solution since I have the exact same symptoms.

[Hoody007]

I am having a similar issue, although my AUX and USB still work. I'm convinced it's a failed TCU in my car, but I have not had a chance to go home and adequately diagnose the issue.

Do you have 6FL (ergo, do you have both AUX and USB in the center console)? If so, then You have two devices handling multimedia, a MULF (for Aux and USB), and a TCU (which handles Bluetooth & BMW Assist).

MOST bus is a fiber optic data net, each module has a receiver and transmitter to keep the MOST bus going. If any module in the loop fails, the entire MOST bus goes down. The red light is this data bus, and the far that its blinking means that something is intermittently taking down the bus.

Here's what I'd do (and what I plan to do once I get back to my car):

1. Buy a MOST bus diagnostic loop
2. Systemically isolate each module by removing the fiberoptic cable from the module in question and connecting it to the MOST loop.

Zspear, what options do you have? The modules in question which are on the MOST bus are the following (some or all may be installed in your car based on the options):

1. Logic 7 amp (in left side compartment, under the gray CD changer cover)
2. TCU
3. MULF / MULFHi
4. Satellite Radio module

The last 3 modules are located in the middle front (portion closest to the front of the car) of the trunk.

The head unit is the "integrating center" of the entire system - it sends, receives, and interprets the MOST signal. You can also isolate the bad module by disconnecting the black MOST bus connector and verifying a red light. If you don't see a red light, then the module before it is the issue.


In all honesty its probably your TCU.

[zspear]

Thanks so much Hoody007! - And my apologies for the late reply. We've been overseas for quite a while. Sadly, the problem didn't fix itself when I came back

I appreciate this a lot. I'm going to get the diagnostic loop and test these components.

Yea, I do have an AUX and USB.

I'll let you know the results and hopefully let you know that I've fixed it.

[askme]

Any resolution or progress on this issue?

[askme]

Any resolution or progress on this issue?