mixersoft

Help–I've got the MMI blues. (Note: This question was also posted here: MMI 2G high not working but not getting any response)

For the last 2 months, I've been cruelly taunted by the MMI startup/welcome screen when I start the car–only to see it completely shutdown after a few seconds. Nothing connected to the MMI system works. Even worse, I can't even use the MMI controller to change the time on the dash clock. Furthermore, if I sit in the car for a few minutes with the car on/engine off, I am again taunted by a short burst of radio music–probably caused by a MOST heartbeat that can't find a satisfactory answer. Then silence. It's maddening to know many individual components are working, but the whole system is dead.

All because I somehow got 1/2 inch of rainwater into the front passenger/right footwell (for a brief history, see: Need help: mysterious water leak and now MMI is flakey). It may have come from the sunroof because i notice the leather shift boot is dry and cracked as if it suffered from water damage.

As it stands, I get a flash of a welcome screen on engine start, and an occasional burst of radio music with the car on/engine off. But no MMI buttons or controller ****.

I read online that this behavior seems to suggest a break in the MOST component ring.

From SSP286 p36, http://www.volkspage.net/technik/ssp/ssp/SSP_286_d1.pdf
"System start (wake-up)
If the MOST bus is in sleep mode, the wakeup process initially switches the system to
standby mode. If one of the control units, with the exception of the system manager, wakes the MOST bus,
it transmits specially modulated light – slave light – to the next control unit. By way of the photodiode which is active in sleep mode, the next control unit in the ring receives the slave light and passes it on.

This process continues right through to the system manager. In the incoming slave light the manager recognises the prompt for system starting. The system manager then transmits another specially modulated light – master light – to the next control unit. This master light is relayed by all control units. Reception of the master light in its FOT informs the system manager that the ring is complete and frame transmission commences."

[img width=633 height=597]https://imgur.com/YzHD1R9.jpg


4F S6 MOST component sequence for 2007 S6
- J523/control unit
- J525/DSP amp w/BOSE
- J533/OBD2 diagnosis interface
- R41/CD Changer
- R36/BT module, Telephone transmitter
- (not installed???) J526 Telephone/Handset
- R/Radio + J507 Voice input
- J401/Nav w CD drive

I also read that you can do a diagnostic scan of the MOST components to identify a component failure. Has anyone ever done this?

Also, my driver "memory seat" isn't working like it used to–front/back adjustments ok, but not up/down. Same with steering wheel adjustment. However, the diagrams don't suggest this has anything to do with the MOST ring. But water damage?

[img width=800 height=440]https://imgur.com/bLwsYbB.jpg
Driver Seat controller diagram
- E97/memory switch for driver seat
- J386/door control unit for driver side
- J136/control unit for seat + steering column adjustment


Best case scenario, I find someone to do a MOST diagnostic scan and discover a failed component. I already checked the BT module under the driver seat, but replacing that with a loopback connector did not solve my problem. My next guess is the MMI Interface Controller (J523/PN 4E0 035 729A).

https://www.ebay.com/p/2007-2008-AUD...29a/2272613008

But before I start blindly buying an replacing components, I thought I'd ask here.

UPDATE: I went to a shop to get a VCDS scan, Diagnosis Manager = Gateway/group 19 > Output Test, but I got an "unable to connect" error. The mechanic thinks this points to an error in J533, PN 4L0907468B or 4L0907468BC. Thoughts?

Any suggestions?

beep-beep

I had the same issue with water in footwell and corroded bt module. Besides replacing the module MOST with bypass I also had to clean up the electric conector since the oxides on it seem to shorten the circuits. I also removed the bt from the mmi config.

JulianHicks

As an A8 owner I don't know what's where on an A6 but here are some thoughts and info. about your points:

The MMI runs in the 'Interface Controller' [aka Control Head / Interfacebox] and is connected electrically to the screen and control pad and optically [via the MOST bus] to the media components in the car. The Control Head also connects optically to the Gateway that connects to the other buses in the car. The Control Head starts up and checks the optical loop; it's one loop and if any part causes a break, then the MMI shuts down. Normally a single media component is the cause but sometimes double failures [two separate devices] can cause trouble as you'd need to isolate them both with an optical bypss so as to complete the loop. Some loop failures on this forum have been to device fuses blown rather than leak problems and amps have been known to go 'short circuit' due to age!

The Gateway doesn't really do anything for the MOST loop other than to be part of it. It doesn't get updated by the MMI CDs but it does run the 'loop test' as it performs an optical and electrical test of the devices on the loop. It obviously needs to be working to perform the test. It and the control head sit in the dashboard. The loop typically runs from the Control Head via the phone under the floor, onto the back of the car where the radio, amp, TV and navigation are and then comes back to the CD player and AMI in the glovebox before going on to the Gateway and back to the Control Head.

Julian

mixersoft

Julian, that is definitely helpful. I'm looking for a strategy in debugging the system. Can I assume that a "Unable to connect" error from a VCDS Gateway/J533 scan means that component is faulty? Can I take it out of the loop with a loopback connector and still expect the system to startup correctly? I also know that the control pad is not working, so that may point to a fault with the Control Head/J523. However, I had not considered the possibility of a double fault -- I need additional loopback connectors to accurately detect.

"Some loop failures on this forum have been to device fuses blown" –– when you say device fuses, are they located with the device itself or in the standard fuse boxes scattered throughout the car. I had already checked all the fuses, but maybe I had made a mistake. A second check might be in order.

JulianHicks

The Gateway "unable to connect" is probably indicative of a fault with that ECU; I've had no experience of that though. Did you get a VCDS log print from that or did you just 'get a verbal'?

Since the Gateway IS part of the loop, a failure may cause its optical connect to 'break the loop' and stop the MMI working. I've not, however, seen anyone describe bypassing that ECU but it's probably worth a go if you can get access to it.

The devices all have individual fuses in the dash ends or the boot/trunk but there's also some 'mega fuses' in the boot/trunk behind and to the left of the battery [they look like large 'metal Is']. Another thread somewhere describes someone who had one of the mega fuses blown that stopped all the media devices in the boot/trunk from working and thus stopped the MMI starting.

Julian

mixersoft

I just spent an hour behind the glove box and the results are inconclusive. This is what I found:

1. Loopback connecter to remove Gateway/J533 from MOST ring: no welcome screen on engine start. seems totally dead
2. Loopback connecter to remove CD changer from MOST ring: welcome screen appears briefly, along with radio, then MMI dark.

So I suppose I can conclude that the Gateway is doing something for the MOST ring, but it's not the source of the problem. I didn't take the Control Unit/J523 out of the loop because it seems pointless. right?

mixersoft

I'm reading this thread https://www.audiworld.com/forums/a8-...923918/page16/ which is giving me some good ideas on how to debug this problem.

But can you give instructions on how to perform this test:



Is that the same as "Diagnosis Manager = Gateway/group 19 > Output Test" which gave me an "unable to connect" error?

kelisko

There must be a short somewhere. One part of the driver's seat adjustment not working for you is what draw my attention. Remove the driver's door panel, disconnect everything in there, try starting the MMI. If it works, you can start isolating components. In my case it was a short in the rear view mirror wiring.

I was involved in an accident which resulted in a destroyed driver's side rear view mirror. I ordered a used one but couldn't figure out how to pass it through the door so I cut the wires and reconnected them one by one. I was stupid enough to use paper electrical tape which was what I had on hand. Everything worked fine. It's been more than a year now. The other day, my MMI started acting. I tried everything I could and lastly I thought of the rear view mirror. I scanned the car and there was one fault in the driver's door. Guess the component, it was the rear view mirror.

When I removed the driver's door panel and disconnected the two connections holding the panel, the MMI started working. I removed the mirror to have a look at the wire, it was a mess. All seized. I was surprised everything in the mirror was still working fine (except the LED underneath that blinks sometimes). I cut the wires again and connected everything back using normal tape this time.

The MMI failed again on my way to work this morning after 5 days of flawless operation. I am going to remove the door panel again and disconnect the mirror at all. I will purchase another one and install it without cutting it when I'm ready.

Try isolating your driver's door. There are a lot of connections in there.

JulianHicks

1. Interesting - looks like bypassing the Gateway stops the MMI for some other reason. But it's not guaranteed that your fault is related to the optical MOST loop, as you've implied the Gateway is problematic. The symptoms of the MMI screen starting and then closing are predominantly caused by loop problems but that may not be the only issue that causes that scenario.
2. Implies to me that the CD is not the source of your problem if it IS a loop problem.

The control unit runs the MMI operating system; taking that out the loop will certainly cause it to not work

To answer your following 'screen shot' post; that test is run by VCDS initiating an Output Test on the Gateway; you can't do it if VCDS can't communicate with the Gateway. You didn't answer my query earlier but I presume you didn't get the output from the failed VCDS test? The output is useful as it gives hardware and software version details as well as some of the configuration settings. If you paid for the test I'd ask them for it; if it was free and done as a courtesy, that request may be a bit more tricky.

Julian

mixersoft

I didn't get the full output from the VCDS test -- it was a courtesy scan.

I also just finished checking all the fuses in the L/R panels on the front dash. Also the rear right trunk fuses. All good. But i checked near the trunk mounted battery and was unable to find anything that would contain a 60A "I" shaped fuse. Any idea where it would be on an S6?