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