[335i_lex]

Hello I will try to keep this quick. I have a 2008 e90 335i non Idrive (business professional RAD2) with Logic 7 SAT and TCU module in trunk only with amp, when purchasing the car in July of 2023 the dash had the SOS error since owning it but audio always worked. In October 2023 I was at work on my break and drove my car then came back to work to sit in the parking lot for a bit and left the car in rest mode where it blows the heat from the engine into the car, this was about a 50 Fahrenheit day. I came back to my car at the end of my shift to absolutely no audio coming from the car including the chimes of course.

The steps I have taken are
Diagnosing via the MOST bus loop I checked all fiber optic connectors including the one beneath the steering wheel and all gave off a red light.

Diagnosing via the logic 7 amp, checked as there was no water or any sort of dampness in the amp area and the car was previously garage kept. There is only the blinking yellow light and a solid red light which from all of my understanding means the AMPLIFIER IS WORKING.

I put an optical loop on every point of the most bus at the same time besides the amp including the bypass loop at the very end beneath the steering wheel incase that was somehow broken. The issue persisted.

I stupidly only ever charged the 6 year old battery instead of replacing and after 2 months of no audio I stored the car in my garage for the winter and left it on a charger, when going to start it the battery was dead as it was 6 years old. I’ve now replaced the battery with a h7 80ah AGM from a lead acid, and coded it to AGM as well as registered the battery. Before even connecting this new battery I had reconnected all modules back being the SAT the TCU and the loop beneath the wheel, to see if when putting in a good battery they would somehow register back. This was not the case unfortunately so I once again tried looping all fiber optic connections in the most bus to try this with the new battery and to no avail.

I’ve also tried disabling the SOS malfunction via bimmercode by entering expert mode of the instrument cluster/kombi and set “TCM_ALIVE_MONITOR” & “TCM_ID_MONITOR” both to “nicht_aktiv” This disabled the SOS malfunction on dash but still no audio.

I've now also attempted replacing the amp with a new used one as it has been 4+ months and have not been able to get anywhere with this, the amp also flashed yellow with a solid red light not fixing the audio. Also I do know blinking amp means that signal is being lost elsewhere but as stated I have bypassed everything and everything also gives a red light without bypassing.

I do not think a mouse chewed through my junction box as there is one case of, I also have not gotten insane intermittent screeching or cuts in audio, to make me refer to the situation of the sunroof module.

Also I have read all links provided here "https://www.e90post.com/forums/showthread.php?t=2074175" by an absolute legend at least once and multiple of them 3x. Any advice, tips, or help would be appreciated more then you know. Thank you if you've read this. I do also have photos of light to each fiber optic each fiber optic being looped and the inner amp lights if anyone would like those to be provided in here.

[ptpending]

if you have tcm alive error then you need to exclude tcu from most loop

[rbryantaz]

I also just had a TCU fail on my e70 and replaced it with a mulf2hi from an e70/e90/etc for $30 or so.

Given that all of the 2G cellular service is no longer available and none of the telemetrics work in 2024 the MULF2 is just an upgrade for the TCM.

I got sound back immediately just plugging it in the MULF2 with no coding with AUX still working through the head unit (but lost hands free bluetooth).

I now need to code it to get bluetooth working through the MULF2 and add 6FL and an AUX wire to have USB and AUX working through the MULF2. I probably won't even use the USB features but need to get the handsfree bluetooth working again.

I believe that AUX through the MULF2 should have better audio quality than doing it through the MASK/CCC/CIC. I read that it is also possible to re-enable the MASK/CCC/CIC to handle the AUX after coding 6FL (which will default it to come through the MULF2) with a coding change but I just bought some good 3 conductor shielded 22ga military wire on ebay and will run that as an AUX line to the MULF2. (correct me if I am wrong about this being "better" audio quality)

One other tip....

I bought a MULF2 that had the blue connector and MOST connectors as cutoff pigtails. I then just slid off the original TCU white outer portion of the connector off from the two sub connectors within it and slid the MULF2 blue one on it. The TCU/MULF wire positions are the same and just the aux wires need to be added. The rest of the CAN wires and others that are not used on the MULF don't cause any issues. Cutting the keys off from the TCU connector would also work but I found a MULF that had the connector for only an extra $5 or so.

I then cut the key off form the MULF2 bluetooth antenna connector on the MULF2 with a utility knife. It was quick and easy and a better option than removing the locking portion of the antenna wire that most seem to do. With this key removed it has a nice snap into place. The other antenna wires on the TCU are no longer needed (I stole the GPS antenna for the android unit anyway).

My e70's bracket that the TCU was on also had an additional mounting provision for the MULF2 including mounting studs and the TCU wires reached that mounting point so no bracket modifications were needed. An e90 might need a different bracket or holes drilled to mount the MULF2 in place of the TCU but that is also very easy and the MULF2 is much smaller so it will physically fit on the TCU bracket with new holes.

I also took the opportunity to just remove my Sirius SAT module and put a MOST bypass from amazon in its place. I had to use the shell of the MOST connector that I got from the MULF2 in place of the one from the SAT connector for the bypass loop from Amazon to fit.

I did this because I noticed that the SAT module was warm so it just seemed like another possible battery drain for something that I don't use (I had already disabled SAT and weatherband in the MASK unit so that I can just switch between radio and AUX with one button push)

My e70 has MASK audio and an android head unit so I can't utilize any of the combox features except perhaps bluetooth audio streaming. I don' think I would use the bluetooth audio streaming because I use the android head unit and use audio from it instead of my phone.

I think MULF2 AUX should still have "better" sound quality than bleutooth. If I had CIC perhaps I would have gone with a combox but I don't see the point of upgrading to CIC when I have the android unit.

I did have some symptoms before my TCU failed that seem to be resolved:

• Audio cutouts for a second or so
• Radio stations would change when shifting into park/drive
• Random chimes would occur for seemingly no reason

-Rich

[335i_lex]

I got sound back immediately just plugging it in the MULF2 with no coding with AUX still working through the head unit (but lost hands free bluetooth).

I really appreciate you taking the time to make this response Rich, the symptoms you had of the audio cutting out for a second on occasion is similiar to what i had noticed and possibly random chimes as well. I will gladly order a MULF2 Hi to replace my TCU if it’ll possibly fix my radio. However I have tried using a bypass loop at my TCU which has still not given audio as well. Also disassembled my amp last night and it was bone dry and looked brand new underneath.
Attached photos of all the loops connected, forgot to take photos of each fiber optic cable end showing light but can guarantee they all do.

[GSB]

Originally Posted by 335i_lex

I will gladly order a MULF2 Hi to replace my TCU if it’ll possibly fix my radio. However I have tried using a bypass loop at my TCU which has still not given audio as well. Also disassembled my amp last night and it was bone dry and looked brand new underneath.

The likelihood of restoring sound by replacing the TCU/MULF is extremely low in your case. Since you have already bypassed every device on the MOST bus, aside from the head-unit and the amp, AND you have the red fiber-optic light completing the ring and coming back to the head-unit, the problem likely lies with the head-unit or the amp.

Note that the radio head-unit can be muted by other devices such as the Roof Function Center (FZD), which works in tandem with the TPU. (See the diagram below). Some time ago, my FZD became contaminated with road pollution, which intermittently activated the SOS feature, which also mutes the radio head-unit.

I've also experienced intermittent "no audio" issues that traced back to previous water damage in the amplifier. You seem to have no visible water damage, but there may still be an amplifier problem. Some people seem to have had success by replacing an amp without coding it, but some of the older amps require coding to restore sound and full communication.

In my case, whenever the sound would cut out, the "Amplifier" module would disappear from the list of devices in the BimmerGeeks ProTool diagnostics app. Running a code scan returned "No Errors", simply because it couldn't even see the amp as a device to check. The MOST bus ring was good all the way, but the ECU/processor in the amp was out to lunch. I was fortunate enough to resurrect my amp because the corrosion on the circuit board wasn't bad enough to cause a dead short that can fry parts catastrophically.