Quote:
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.
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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.