Hey,

I have a problem with this code from VCDS.
I checked the fuse box and its ok. I connected the MOST male and female to this device ( yellow) and nothing


Address 19: CAN Gateway (J533) Labels:. 8T0-907-468.clb
Part No SW: 8R0 907 468 P HW: 8R0 907 468 D
Component: GW-BEM 5CAN-M H11 0055
Revision: 1Z100027 Serial number: 2741Z12B130156
Coding: 80C303FF00
Shop #: WSC 06335 000 00000
VCID: 4C97D137EFCB1EEF63-8018

Subsystem 1 - Part No SW: 8R0 915 181 HW: 8R0 915 181
Component: J367-BDM H07 0141
Serial number: 00000000003790541331

00384 - Optical Databus
011 - Open Circuit
Freeze Frame:
Fault Status: 01101011
Fault Priority: 5
Fault Frequency: 1
Reset counter: 33
Mileage: 170819 km
Time Indication: 0
Date: 2023.11.13
Time: 16:44:22

Freeze Frame:
Bin. Bits: 10000
Voltage: 12.00 V
Count: 11
Bin. Bits: 00000



Where to watch first?

 

This is what the optical ring (MOST bus) looks like for MMI 3G. J794 is the unit at 5F, mounted in the dash above the climate controls. Says "Audi multimedia". R is the 56-radio, in the left rear (this is also the amp if not B&O). J525 is the 47-sound system (amp), in the left rear (if B&O sound system). J533 is the 19-CAN Gateway. Inside the dash between the glove box and the J794.

The error says the ring is broken. As you see, the ring goes in and out of each device in sequence. If there's any issue with any of the devices, they will be down, the ring will be broken. Placing the male loopback plug onto any of the devices is meaningless except for the J794. That is the only device where the loopback plug is effective, because the J794 is the ring master. Without the J794, there is no ring. Placing the female bypass plug onto the cable that would plug into any of the devices is a legit means to test if that device is breaking the ring. But again, no J794, no ring, so putting a bypass loop on the cable to the J794 is pointless.

The ring break diagnosis reports electrical error for the radio and the J794. You need to confirm good 12v from the 12v pin to the ground pin on the plug that goes into the radio unit (large red/violet wire to large brown wire). If the voltage supply to the radio is good, one has to wonder why the radio is not reporting back during the ring break diagnosis. If there was an electrical issue with the radio, the bypass loop on the optical cable to the radio unit should isolate that and allow MMI to stay up (though obviously with no radio audio).

But you also have an electrical error for the J794. It also uses a fuse in the right rear. You'd need to dismount the J794 from the dash and likewise validate it has proper 12v as well. If the 12v is good to it, you should put the male loopback plug directly onto the J794 and see if it stays up (display on screen stays active). If not, then something is not well with the J794.

 

Thank you for answer. I had a problem with fresh air blower so I have open glovebox like this. It will definitely be easier to check cables.

I think about changing standard MMI display to newer android with carplay.

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"You need to confirm good 12v from the 12v pin to the ground pin on the plug that goes into the radio unit (large red/violet wire to large brown wire). If the voltage supply to the radio is good, one has to wonder why the radio is not reporting back during the ring break diagnosis. If there was an electrical issue with the radio, the bypass loop on the optical cable to the radio unit should isolate that and allow MMI to stay up (though obviously with no radio audio)."

Is there any option to check this 12V via VCDS? Or just the option of disassembling the dashboard and check this two devices?

 

Where did I say the radio was located? It's not in the dash, nor is the amp. They are elsewhere and easy to access. You already posted a picture of it in the opening post. What is all the yellow on it?

You're not interesting in what the control module is reporting for voltage at this point, you're interested in what you independently measure using a meter. With the ring down, you can't get to the control modules anyway.

You see the J533 there with the red connector in your second pic. You'll need the MMI removal keys to remove the J794 from the dash above the climate controls.

 

From the beginning. I checked all the fuses and they were ok. I opened the trunk and found the radio module on the left side? It's painted yellow.
There I connected the female and male MOST. It didn't help.

I don't have access to the amp , there's not enough space. This is the one next to it on the right and the entrance is at the back.
Should I unscrew the access to the amp ( MOST), or should I start by removing the Audi Multimedia from the front and the red cable from the glove compartment?

I'm new to this and I don't know where anything is or what doesn't work.


On Multimedia I see a optic cable



and this is the second device on glove box

 

As I said in my first response, putting the male loopback plug onto anything but the J794 is pointless. That you put the female bypass plug on the optical cable and things still didn't work means the radio may or may not be a problem, but you have problems elsewhere additionally. That the ring break test reports an electrical fault for the J794, you need to be looking at that device. I don't thing there's anything you need to look at with the J533, the gateway, the device next to the glovebox with the red plug.

Put the lookback plug onto the J794 (the device in the dash above the climate controls). Either the MMI display is going to come up or it won't. But at that point, there is no MOST ring except that piece of orange plastic going from the J794 Tx port to the J794 Rx port. So if there's still an issue with MMI coming up, it's wholly an issue with the J794, or maybe the J685 display (should be easy enough to see if the display appears to be working, does the Audi logo at least come up at power on) or the E380 controls.

 

Wouldn't it be easier to just buy an Android car and replace the entire unit? Removing Audi Multimedia and the display is not difficult.

 

Then you have no means to interact with the CAR menu. Aftermarket solutions of that type sit between the J794 and the screen. They do not replace the J794. And they also require the factory sound path to be working, as they are not a preamp for the factory amp solution. They have an output the factory system must accept as an external input. And the J794 is the ring master. No J794, no optical operating in the car.

 

Shouldn’t be more fuses in the trunk?

 

This is B8.5? No, column "A" is only for special purpose vehicle systems (radios and such). And "D" is not used at all. We see the four in "E" there, for the MMI 3G J794, the MMI 3G radio (B&O config), the backup camera J772, and the rear window defogger relay J9, which should be off to the right of your image.

B1 and C1 are for the rear lid motors
B2,B3,B4 for the towing module J345
B5 for the elec. parking brake button E538 (not sure why the button needs a fuse)
B7 and C7 for the elec. parking brake motors
B8,B10 for the rear tail lights via the J393
B11 for the J393
B12 for the fuel tank leak detection module (EVAP)

C2 for the 12v sockets relay (should also be there off to the right)
C4 for the amp (B&O in this config)
C8 for the rear heated seats
C9 for the right front door
C11 for the right rear door