MMI not working

[hiwasss]

I started the car this morning and the screen stayed off. None of the buttons on the MMI unit are lit. When pressing mode button on the steering wheel it doesn't change to another menu. There is no audible coming from the rear camera and I ran a full disagnostic but nothing related this problem is flagged. I did try to hard reset the MMI module without luck.

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[byront8]

Have you run a optical loop test? In case one of the units isn't working over the MOST?

[hiwasss]

Have you run a optical loop test? In case one of the units isn't working over the MOST?

I'm not familiar with the procedure, can you explain how it's done? I assume I would need one of these?
https://www.amazon.com/optical-bypass-adapter-MERCEDES-PORSCHE/dp/B01FREU5F8

[byront8]

I'm not familiar with the procedure, can you explain how it's done? I assume I would need one of these?
https://www.amazon.com/optical-bypass-adapter-MERCEDES-PORSCHE/dp/B01FREU5F8

So if you have VCDS, you can run this procedure - https://www.ross-tech.com/vcds/tour/optical-bus.php

Sometimes one of the units has the MOST fail and so the rest of the system won't start as its not a complete loop.

[RyanWysong]

Had this same issue in the past, it ended up being my radio receiver in the left trunk compartment or also considered the amplifier if you have Bang & Olufsen I believe. You can test the MOST system by plugging in the optical bypass loop shown above into the connection that would normally go into the amp. In my case, my MMI fully came back to life using the bypass but I had no volume from my radio/bluetooth etc, only sound that would occur is the beeping when the car was in reverse. I purchased a used radio receiver on eBay from an a7 for roughly $250, installed myself and paid the dealer to program it into my s4. I believe this is a common problem with the s4's due to moisture getting onto your amp. Hope this helps.

[hiwasss]

I had a chance to check the optical signals in the trunk and this is what I found. There is no light on the optical cable that goes into the amplifier but the optical cable that goes into the jukebox is lighted.

I plugged the MOST optical bypass loop female adapter into the cable that goes into the amplifier but my MMI still won't turn on and no music is available. Are there other modules that would take an optical signals I'm not seeing? I did check the fuse for the MMI on the front passenger side and the fuse is good.

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[Gunnark100]

I had a chance to check the optical signals in the trunk and this is what I found. There is no light on the optical cable that goes into the amplifier but the optical cable that goes into the jukebox is lighted.

I plugged the MOST optical bypass loop female adapter into the cable that goes into the amplifier but my MMI still won't turn on and no music is available. Are there other modules that would take an optical signals I'm not seeing? I did check the fuse for the MMI on the front passenger side and the fuse is good.

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Did you restarted(or at least ignition off on again) car after plugging loop?
Also check fuses for radio and amplifier in the trunk.
Also check radio unit with bypass loop in the trunk.(if you have bang)

[hiwasss]

Did you restarted(or at least ignition off on again) car after plugging loop?
Also check fuses for radio and amplifier in the trunk.
Also check radio unit with bypass loop in the trunk.(if you have bang)I did start/stop the car after I plugged the optical cable to the bypass cable. I didn't see any fuse box in the trunk, I checked the fronts on the driver and passenger side and none of the fuses are blown. I don't remember seeing anything in the trunk beside the amplifier and jukebox. I have B&O speakers if it makes a difference.

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[Gunnark100]

delete