Mercedes M Klasse hands free microphone issue

That sounds frustrating! I had a similar Bluetooth issue with my old Volvo V70, though not exactly the same. My audio input would randomly cut out during calls. Did you check the microphone itself to see if it's visibly damaged or obstructed? It's probably deeper than that with an error code, but I thought I'd ask. Did you try resetting the infotainment system? Sometimes that's all it takes. Who designs these systems anyway?

When you mention resetting the infotainment system, how did you do that? Also, were there any symptoms before the audio input failed completely? I want to see if our experiences are similar.

On the Volvo, I just held down the power button for about 30 seconds. It was a total shot in the dark! It started with the sound quality getting really bad, like muffled, and then it would just cut out completely. Eventually, the voice recognition stopped working altogether. Since you're getting an error code and it's a Mercedes, it's probably beyond a simple fix. It sounds like the infotainment system is genuinely broken and you will have to get it checked at the workshop.

I consulted with a technician, and they confirmed the infotainment system is defective and needs replacing. The total cost was 815€. Thanks for the help.