Looking for input. MMI repair

[Eddyson]

Hi all, I’m hoping can someone provide some clarification.. I’ll try keeping this short, mmi system won’t turn on.
Dealer diagnosed to replace 5F module. $7300 CDN quote for just the part lol
I sourced out a second hand part and had my mechanic install.
Original part # for my 2013 S4 is 8R1 035 664C.
The part I found is the same aside from the last letter ending in C, the one I found ends in F from a 2015 a4.
Part was installed and still mmi won’t turn on.
My mechanic thinks my original 5F unit is fine and that the trunk mounted radio module is the problem.
He is using vagcom to diagnose.
I phoned the dealer and they disagree. They say the 5F module must be 8T1 035 664C in order to work.
Is this true?

[elscotto80]

I'd guess you need to remove component protection for it to work, if it's the correct part.

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[Eddyson]

Yes this is true. We haven’t made it to this point yet. Even with the replacement 5F installed the screen still won’t turn on.
The system needs to run in order to remove component protection.

[f1torrents]

Yes this is true. We haven’t made it to this point yet. Even with the replacement 5F installed the screen still won’t turn on.
The system needs to run in order to remove component protection.

This is not correct.
With active CP the system will NOT turn on.

[Smac770]

All control modules with component protection aspects will turn on and be able to communicate. The CP exhibit for the MMI 3G era J794:

The information electronics control unit -1- J794 has a component protection feature. When the component protection feature is active, all audio outputs entertainment sources are muted. A message text is displayed on the MMI display when the system starts. The audio outputs for telephone and navigation announcements remain active.

If the J794 is shutting down, it could be the J794 or it could be the MOST bus. Just plug a male bypass loop onto the back of the J794 (the the J794 out loops right back into its in) and see if it runs without any of the car's MOST bus cabling or slave devices (radio R, and if installed, sound amp J525). (not tried it before, just seems the obvious thing to isolate external bus components; you could put female bypass loops on the loop plugs at the radio and J525, but that keeps any in-car optical cable issues in play).

It's not going to be an 8T... unit for B8.5 MMI 3G+. 8T... J794 are for MMI 3G in B8.0. For MMI 3G+ in the B8.5 for USA (PR-8DY), it'll be 8R1 035 664 for the version without the sim card slot and 8R1 035 746 for the version with the sim card slot. The revision letter in this specific case directly relates to when the unit was installed. Later revisions will be newer software, maybe any hardware updates. But a C or a F, you're going to apply the latest MMI firmware and navigation updates to either. C was used Nov '12 through May '13 (so later MY13 builds). F was used late May '14 through Oct '14 (so earlier MY15 builds).

[Eddyson]

All control modules with component protection aspects will turn on and be able to communicate. The CP exhibit for the MMI 3G era J794:



If the J794 is shutting down, it could be the J794 or it could be the MOST bus. Just plug a male bypass loop onto the back of the J794 (the the J794 out loops right back into its in) and see if it runs without any of the car's MOST bus cabling or slave devices (radio R, and if installed, sound amp J525). (not tried it before, just seems the obvious thing to isolate external bus components; you could put female bypass loops on the loop plugs at the radio and J525, but that keeps any in-car optical cable issues in play).

It's not going to be an 8T... unit for B8.5 MMI 3G+. 8T... J794 are for MMI 3G in B8.0. For MMI 3G+ in the B8.5 for USA (PR-8DY), it'll be 8R1 035 664 for the version without the sim card slot and 8R1 035 746 for the version with the sim card slot. The revision letter in this specific case directly relates to when the unit was installed. Later revisions will be newer software, maybe any hardware updates. But a C or a F, you're going to apply the latest MMI firmware and navigation updates to either. C was used Nov '12 through May '13 (so later MY13 builds). F was used late May '14 through Oct '14 (so earlier MY15 builds).

Thank you for all the information.
I meant 8R1 035 664 C when I made the comment that the dealer said only this part will work in a 2013 S4.. the 8T1 was a typo. I didn’t realize I made the error, thank you.
We tried by passing all three modules individually and still MMi wouldn’t turn on.
So if I understand you correctly, the unit ending in F should work fine in my car? I mean the mmi should at least turn on and then CP can be removed…

[Smac770]

The F unit is at a minimum going to start up just fine if it's functional, I would expect. You either have a bad unit or a break in the optical (MOST) bus. And when you say it doesn't turn on, you see a splash screen and then it goes off? Or you never see anything? Do you hear the hard drive spinning? It blows my mind, wait, Audi, no it doesn't, that there's no hard line diag connection to the J794. The only way to talk to the J794 for diag purposes is to go over the MOST bus from the J533 to the J794. Stupid, if the optical bus is having an issue. Apparently there is a means to establish a serial connection to the console port, but you have to solder on a serial port first, joy.

Passing all three modules, ..., meaning? There's the radio R; you can use a bypass loop on the cable plug to bypass the radio. There's the amp J525, you can do the same there. There's the J533, in the center stack, behind the glove box. Then there's the J794 in the center stack in the dash. If you wanted the minimum involved components, you'd run a direct cable from the J794 to the J533, establishing a loop between those two device using none of the in-car cabling. The J794 will not operate with nothing in its optical port; that's a broken ring.

The display is known good? I don't have MMI 3G so I can't experiment first hand. I would wonder if the MMI would go down if detecting a screen interaction failure.

It's annoying that J794 problems would be blatantly obvious if they just had a hard line for watching the boot log. But Audi goes out of their way to make sure field repair is as impossible as possible.

[Eddyson]

The F unit is at a minimum going to start up just fine if it's functional, I would expect. You either have a bad unit or a break in the optical (MOST) bus. And when you say it doesn't turn on, you see a splash screen and then it goes off? Or you never see anything? Do you hear the hard drive spinning? It blows my mind, wait, Audi, no it doesn't, that there's no hard line diag connection to the J794. The only way to talk to the J794 for diag purposes is to go over the MOST bus from the J533 to the J794. Stupid, if the optical bus is having an issue. Apparently there is a means to establish a serial connection to the console port, but you have to solder on a serial port first, joy.

Passing all three modules, ..., meaning? There's the radio R; you can use a bypass loop on the cable plug to bypass the radio. There's the amp J525, you can do the same there. There's the J533, in the center stack, behind the glove box. Then there's the J794 in the center stack in the dash. If you wanted the minimum involved components, you'd run a direct cable from the J794 to the J533, establishing a loop between those two device using none of the in-car cabling. The J794 will not operate with nothing in its optical port; that's a broken ring.

The display is known good? I don't have MMI 3G so I can't experiment first hand. I would wonder if the MMI would go down if detecting a screen interaction failure.

It's annoying that J794 problems would be blatantly obvious if they just had a hard line for watching the boot log. But Audi goes out of their way to make sure field repair is as impossible as possible.

No the screen won’t turn on at all.
Leading up to this, the screen would turn on but then shut down after a couple minutes.
Now it won’t turn on at all.
We installed a new HD and still MMi wouldn’t run so we ruled out a failed HD.
We bypassed the 5F, radio, and amplifier individually. I didn’t know the b8.5 had another module behind the glove box.
Should we try bypassing the j533?

[Gunnark100]

No the screen won’t turn on at all.
Leading up to this, the screen would turn on but then shut down after a couple minutes.
Now it won’t turn on at all.
We installed a new HD and still MMi wouldn’t run so we ruled out a failed HD.
We bypassed the 5F, radio, and amplifier individually. I didn’t know the b8.5 had another module behind the glove box.
Should we try bypassing the j533?

Did you restart a car after each isolation? Cant believe that gateway(j533) is dead!

[Smac770]

You can't bypass the J794, it's the MOST bus master. Without it, there is no ring.
The J533 is on the bus for the purpose of ring-break diagnosis, but it serves no leadership role in the execution of the MOST topology. That said, I don't know if the J794 will see a lack of comms (via the MOST bus) to the J533 as a motivation to abort boot.
Putting a female loop plug on the cable going to the J794 and leaving the J794 unplugged will certainly just make the J794 abort boot. So bypassing the J794 would require a male loop plug plugged in to the back of the J794. But I've never tried that so I can't say that it'll establish a working ring from the J794 processing perspective, either.
What were the electrical and optical results from the ring-break diagnosis using VCDS?

[Eddyson]

Did you restart a car after each isolation? Cant believe that gateway(j533) is dead!

No we didn’t restart the car after each module bypass.. I didn’t think it would make a difference.
The aux ignition was on/off for each test but not engine running.

[Gunnark100]

No we didn’t restart the car after each module bypass.. I didn’t think it would make a difference.
The aux ignition was on/off for each test but not engine running.

Ignition on/off has same effect,no need to run engine,anyhow a bit strange story...any chance that other main unit you got is also faulty?

[Eddyson]

Ignition on/off has same effect,no need to run engine,anyhow a bit strange story...any chance that other main unit you got is also faulty?

It’s possible the replacement unit would be faulty.
We also tested a third 5F unit, this one was from a Q7 but all the connections at the back are the same and still no luck..
The odds of all 3 5F modules being defective are very low.

[hardfive]

This is not correct.
With active CP the system will NOT turn on.

Incorrect. For anyone reading this CP mutes audio from the unit it does not disable the display.

[Gunnark100]

No the screen won’t turn on at all.
Leading up to this, the screen would turn on but then shut down after a couple minutes.
Now it won’t turn on at all.

As you tested few units etc...please double check MMI component fuses including those in trunk, not first time when during tests etc those blow up...maybe lucky :)

[Eddyson]

As you tested few units etc...please double check MMI component fuses including those in trunk, not first time when during tests etc those blow up...maybe lucky :)

This was the first thing I checked. All fuses are good.
I found a mmi module for sale. Exact same part number as my original.
Before I purchase another one. The seller mentioned that anytime a module is replaced, because the new part has a different serial # than what the car recognizes. You will need to marry the new replacement unit by burning the old serial number and programming the car to recognize the new #… without doing this step, even a brand new module will not work..
Can anyone confirm this?

[Gunnark100]

This was the first thing I checked. All fuses are good.
I found a mmi module for sale. Exact same part number as my original.
Before I purchase another one. The seller mentioned that anytime a module is replaced, because the new part has a different serial # than what the car recognizes. You will need to marry the new replacement unit by burning the old serial number and programming the car to recognize the new #… without doing this step, even a brand new module will not work..
Can anyone confirm this?

Smac and others answered already to this question....in short sellers statement is BS, system will run and must boot up, just functions are limited!

[hardfive]

This was the first thing I checked. All fuses are good.
I found a mmi module for sale. Exact same part number as my original.
Before I purchase another one. The seller mentioned that anytime a module is replaced, because the new part has a different serial # than what the car recognizes. You will need to marry the new replacement unit by burning the old serial number and programming the car to recognize the new #… without doing this step, even a brand new module will not work..
Can anyone confirm this?

I ran a replacement MMI for 2 months before I got CP removed. It booted up just fine, it just mutes the audio and the different screens tell you theirs an issue and you need to go to the dealer.

If you have no video its 100% not CP.

[kelseysautobody]

Hi all, I’m hoping can someone provide some clarification.. I’ll try keeping this short, mmi system won’t turn on.

Did you ever resolve your problem? Running into similar issues.

[Fresh.S4]

ive got extra b8 trunk hardware...

[JeeprageII]

Did you ever resolve your problem? Running into similar issues.

How about you? Did you fix yours? Same issue started today for me.