A4 B6 Network Control Unit Malfunction? Is a test possible?

Hello everyone,
I am a beginner in the field of modern vehicle tax technology and would like help from those who are definitely experts!

Vehicle:
Audi A4 B6 1.9 TDI 98KW, Year 2002

Since Saturday, it's been essentially a complete failure...
Symptoms:
- ABS, ESP indicator lights do not turn off after engine start
- All steering functions (indicators, headlights, power windows, windshield wipers, etc. not functioning)
- Side windows cannot be opened/closed
- Side mirrors not adjustable
- Sliding roof not adjustable/openable
- Climate control unit with no function

What I did:
At the ignition switch (positive wire connected to the radio, negative wire disconnected).
I have switched on a relay because I don't know what power the car radio draws through this connection.

All fuses have been checked. Status: OK


Question:
- Am I right in suspecting a faulty central control unit?
- How can I specifically find this specific tax device?
- Can I use VCDS to check the functionality of the device, and if so, how?

Hoping you can help me!!!!
Thank you in advance for your support.

Do you have an old scan?
The vehicle should have significantly more airbags, or is it really that bare?
Motor reports missing climate control unit. Climate-STG doesn't even appear on the list.

I'm not familiar with that particular vehicle, but I assume you're referring to a central fuse. The most likely candidates would be one of the main fuses or the Maxi fuses. Does a 2002 model have a fuse box next to the battery in the engine compartment? If so: Have you also checked the fuses that were screwed in from the front?

Greetings
Guste

First of all, thank you for the feedback, Guste!

I bought this great piece last year in September and then checked the error memory to see what was stored there. So, there's still something!
Regarding the errors that occurred, such as:
1 Error found:
01331 - Driver's Side Door Actuator (J386)
49-00 - No communication ... etc.
I didn't spend much time considering different {SSL/TLS} options back then (naive, ignorant?), since everything had been working fine so far.
The seller was a young guy (not meant to be malicious!), who probably used the car as a DIY project. This means he probably installed illuminated strips in the doors and dashboard (like in high-end cars) and the problems might be due to this, along with many other minor issues. But, as I said, everything was fine.

In the attachment, you will find the scan from September...

Fuse boxes? Hmm, I'm not sure where these should be located. I've checked all the 40, 50, and 60-amp fuses in the fuse box located in the driver's footwell. They are all in good condition. Besides the battery, I haven't checked the fuses yet; I haven't seen any fuses there before, but I will check again tomorrow.

Unfortunately, I do not have a wiring diagram for the vehicle's electrical system.

I will be able to say more about the fuses tomorrow.

Greetings. Jürgen

Out of the nine Steuergeräte from the old scan, four STGs are now found. Obtain the wiring diagrams for your vehicle (which can be downloaded for a one-day fee directly from Audi / ERWIN). Then, check the five STGs for similarities. I am quite certain that everything is converging at a single point.

Edit: Since you've been messing with the ZAS, it would probably be helpful to check there first, while the engine is running, to see if there's actually voltage on all the pins (except the starter contact). If there is no voltage on a pin, I could imagine a similar error scenario.

If I haven't fallen in love while flying over it, then it might be that contact 75 or the X-contact is broken.

Greetings
Guste

Okay, I've just tested the ZS, and guess what... Is everything okay?
I obtained the schematics from Audi, but I have little experience in reading electrical diagrams. It's not that difficult, except for a few fundamental symbols and representations that I'm not familiar with.

However, to my understanding, at least, it seems that the STGs are more or less serially connected. ZS - Steering Column Module - Bus Network - Comfort and including Climate Control and Doors.
After everything was okay at the ZS, I tried to measure something on the LSM connectors (if that was even possible), and to my surprise, the connector for the LSM was loose and had no contact!!!
May ashes fall on your head!! Sorry, absolutely embarrassing!!
I definitely didn't have it in my hand, and besides, this plug doesn't have a locking function.
Stuck in and everything is back to normal.

I would like to thank you, Guste, for taking on the problem. Without your advice to check the ZS, I would never have found the issue with the plug!! The mechanics would probably have just replaced all the STGs for me first. Okay, thank you again...

@Admin: Maybe delete this thread, it's actually a disaster

Why delete? You described an error and found a solution. Maybe it will help someone else someday too. No locking mechanism? Is the plug damaged?

I have to admit, I didn't really look closely at the plug to see if it was damaged...
... only to the extent that, plug in - no problems - unplug without any issues! and then plug it back in.
However, the seat is "sucking". For further review, the feeling of euphoria was too intense .
Along the steering column mechanism, there is a "cable collecting" plastic strip that is attached to the adjustment unit of the steering column. I removed this to be able to correctly identify the cable 86s Pin8 Red (Switched Plus when the key is still inserted!! for the Nix-Audi radio installers). By the way, I probably unplugged the LSM, BECAUSE NOTHING WAS COMPROMISED .
"In any case, all STGs reappear in my Autoscan file, and all the error codes have disappeared!!"
Greetings to everyone...