When I purchased the car, I had some minor but annoying issues:
SOS - Inactive Warning
Bluetooth not working
USB and AUX plugs in center armrest had no power/signal
It was frustrating not being able to make phone calls through the car's speakers, and not being able to play music.
I'm not an electronics guy but through some research found that any interruption in the MOST fiber optic system will cause multiple failures. Similar to the Christmas light bulb effect, when one dies they all die. My symptoms weren't that bad, but I did purchase a fiber optic loop jumper that allowed me to bypass modules one by one until I stopped having problems.
Once I jumped the MULF2 module (located on the trunk floor on the right side, under the TCU module), the Bluetooth came back and I was able to pair my phone. The SOS warning also went away. Success!
That meant that there was definitely an issue with the MULF2 module, so I found a used one on ebay for $50 and installed it. The SOS warning was permanently gone, the Bluetooth capability was restored, and the biggest victory was the AUX coming back. It was so motivating seeing the AUX volume bar moving, rather than being stuck at zero like it had been for so long. The USB port in the armrest also had power again.
The only thing that was left was the 12V power port in front of the shifter - again, no power. This is a simple power port that doesn't use any modules for activation, just a simple fused circuit.
I dug open the glove box to find the fuse panel...
Consulted the diagram which was neatly folded in the cover
Found Fuse 08, which controls accessory power
And removed it for a closer look, compared to a known good 20A fuse.
My assumption is that at some point someone dropped a coin into that power port and shorted it, which blew the fuse.
Next up on the list is some performance testing, test pipe install/modifications, and some general maintenance/inspections.
Oh, and check out this E30 M3 I saw at my workplace...
