Need help with my B8’s MMI.

[prest0]

Hey all

I just recently got my hands on a higher mileage S4, and it’s great but I’m having issues getting the MMI to work. It has the B&O system, and nav. When I got it, it would just show the splash screen & nothing else. Then I bought a pair of optical loops, and when connected in place of the radio module, the MMI would boot and work with the exception of no sound (except parking sensors and hands free/nav? bluetooth calls work no problem). Now, I have bought a used module on ebay from an S5 of the same year with the same system. It will not boot up. Just back to splash screen. No lights or anything. Any guidance would be appreciated. I don’t have access to VCDS yet but will soon.

[Smac770]

Assuming you have MMI 3G High, if B8.0, or MMI 3G Plus, if B8.5, then there's only four components on the MMI ring, since you have B&O.

J794 (dash unit that says Audi multimedia, this is the main infotainment system unit)
J533 (gateway unit that bridges the MOST ring members to the rest of the car)
radio (the radio unit in the left rear)
J525 (the amp if you have B&O, also in the left rear)

That's it, two in the dash, two in the left rear.

If you loop out the radio and amp, and you have issues still, you're likely looking at a failed J794, or some issue with one of the components directly connected to the J794. That's the E380 controls and the J685 display.

But your first observation is you said you looped out the radio unit (or did you mean the amp unit?) and the MMI system would operate. Ok, so what then did you replace? The radio unit? Or the amp unit? If you loop one or both out, MMI returns to working again?

What specific model year vehicle is this?

[prest0]

Assuming you have MMI 3G High, if B8.0, or MMI 3G Plus, if B8.5, then there's only four components on the MMI ring, since you have B&O.

J794 (dash unit that says Audi multimedia, this is the main infotainment system unit)
J533 (gateway unit that bridges the MOST ring members to the rest of the car)
radio (the radio unit in the left rear)
J525 (the amp if you have B&O, also in the left rear)

That's it, two in the dash, two in the left rear.

If you loop out the radio and amp, and you have issues still, you're likely looking at a failed J794, or some issue with one of the components directly connected to the J794. That's the E380 controls and the J685 display.

But your first observation is you said you looped out the radio unit (or did you mean the amp unit?) and the MMI system would operate. Ok, so what then did you replace? The radio unit? Or the amp unit? If you loop one or both out, MMI returns to working again?

What specific model year vehicle is this?

Hi, sorry for the late reply.
It’s a 2012 S4 Prestige. I think it’s the radio module. It’s in the trunk, left side. On top is the amp and below it is the radio module(?). If I hook the optical plug that goes into the radio receiver into a loop, my MMI works perfectly. Just no audio, no volume adjustment. I can very faintly hear music on MDI output if I move to options and go to the “adjust in car entertainment audio” menu, but it’s very very faint. I bought a used model on ebay. (part number 638-52124) and the MMI doesn’t boot at all when plugged into it. If I do the 3 button reset I can hear the HDD click as it restarts but nothing else. With the amp connected and the radio module looped, everything works, I have nav audio and bluetooth call audio but nothing else.

[A4Qwattro]

Sounds like component protection kicked in? That module is coded to the S5 that it came from. It won’t work in your S4 even if it has the same part number until dealer removes the component protection. It’s an anti-theft measure.

If you scan with VCDS, you with see that component protection in the faults.


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[Smac770]

"638-52124" is not an Audi part number. So this was a replacement radio unit?

So your original radio plugged into the optical, MMI doesn't work?
And replacement radio plugged into the optical, MMI doesn't work?
But the radio unit optical plug, plugged into a bypass loop, MMI works fine?

So either your radio unit is bad, and you bought a dud replacement. Or the issue is not the radio unit; maybe power to the unit. Did you confirm 12v present on the hot to ground wires on the big connector? If you have B&O and all the speakers connected to the amp, there's probably very few wires on the radio unit plug. So the brown (ground) and red/violet (fused 12v). If you don't measure 12v present, check the fuse, should be right rear, column E, fuse 5. Probably a 5A.

[prest0]

So, I changed the fuse out that you said and it turns on now with my original radio hooked up (yay!). Now, I still don’t have any audio besides nav and bluetooth calls. What should i do now?

[Smac770]

When you say "besides nav", so you do actually hear audio output from the sound system when the source is nav and handsfree? Ie, the full signal path to your ears does in fact work?

If entertainment sources have been muted, it's likely component protection (CP). Have you tried other entertainment audio sources, like the CD and the AMI (glovebox port)? If it's all entertainment sources, probably CP. If it's only radio sources (AM, FM, Sirius), it's probably still more issue with the radio.

But you really need to scan with VCDS and see what the actual problem is; it's a lot of random guessing without that.