Replacing the AFN control unit in an Audi A4

Hello everyone.

I'm new to the forum and already have a question for you all.

I have an Audi A4 TDI, manufactured in May 1998, with an AFN engine and a manual transmission, and I need to replace my timing belt.
The original EDC MSTG has the part number 038 906 018S, Bosch number: 0281 001 721. It does not have ESP/ASR but is defective.
I have one with the number 028 906 021GN, and it's currently installed and working.
"However, since a chip was installed, the air conditioning system no longer works. The AC system has been checked, and all individual components (control panel, compressor sensor, etc.) are functioning correctly."
I would like to install a different MSTG for testing purposes, and my question is which other MSTGs would be compatible or if I should only use one with the original part number.
I would be very grateful for your answers.

Pedro33

Are you sure about the numbers? 038 906 018S is normally not replaced, and an identical one should fit. It should have 2 connectors and an external MAP sensor. } The 028 906 021GN should be an even older model with an internal MAP sensor and only one connector. } That probably won't fit at all.

Hello.

I bought the MSTG 028 906 021GN a year ago from a car appraiser in Berlin. I was told at the time that it should fit. This MSTG is also an EDC15 version (with 2 external MAP sensor connectors). I recently inquired with , and they explained to me that this number also exists for Skoda vehicles. Apparently, Audi also used units with a similar number (old MSTG) in models from 1995/1996. The MSTG has been installed for a year and has worked perfectly until now, but then a chip was installed. Since then, the problem with the air conditioning has appeared. Therefore, I would like to try a different one. The part number 038 906 018S is difficult to find; I have been searching for it for some time and don't want to spend 300-400 euros on a used one.
Best regards,
Pedro33

I cannot associate this number with Skoda. '028' sounds more like an older MSA (Motor System Area). Are you sure that only the sticker on the control unit is present and that the contents are not different?

@Pedro
Please take a picture of this 021GN.

Best regards, Micha.

Hello everyone.

I re-read the MSTG module using VAG-COM.

Part number: 028 906 021 GN, Component: 1.9 R4 EDC 20 SG 1422.
I did take a picture, though.
Unfortunately, VAG-com doesn't know how I can insert it here.
It's possible that this part was used in Seat vehicles instead of Skoda, and I might be mistaken here.
A friend of mine also has the same device number on his A4, which is a 1997 model. I was surprised that both cars could have the same number even though they have different versions of the MSTG (Modular System Technology).

Pedro33

I believe you wrote down the VAG-COM number correctly .
Sure, here is the translation of the text from German to English:

"The images are not necessary."
I'm more interested in a picture of the control unit.
If it actually has two plugs, someone must have taken the data from the old...
Audi STG plugged in.
There was nothing like that before!

Best regards, Micha.

Hello Micha,

I'll try to post a picture of the MSTG here.
But you can believe me when I say that I know what the old and newer control units look like. I even have one of the old ones at home if anyone needs it; the part number is 028 906 021 CE.
Old version: 1 large connector / internal map sensor.
You're not entirely wrong with your suspicion that the data sets might have been altered. I happened to meet someone today who knows a friend at the Technical University of Vienna, and I was able to talk to him on the phone. He's familiar with VW-Audi engines and also believes that something fishy is going on here. He explained to me that my problem with the air conditioning might also be caused by the MSTG signals being processed incorrectly, which can lead to the compressor being shut off.

Best regards,
Pedro33

I'm afraid you have the solution.
The MSA15.7 contains an MSA15.5 dataset!
Since the processor core of the late 15.5-inch models and most of the 15.7-inch models is identical, it runs...
Generally speaking, the software is good. However, the assignment of inputs and outputs is incorrect.
100%.

put in the appropriate dataset.

Best regards, Micha.

Hello Micha,

Sorry for getting back to you now.

You were absolutely right about the incorrect datasets. The tuner installed the wrong chips in my car. MSTG is already the correct one, but he installed the wrong chip.
I had a chip with the correct part number at home, so I tried it. Sure enough, the air conditioning is working again, and the engine runs more smoothly. However, these chips are just cheap tuning parts from eBay. I'll be visiting a chip tuner in the next few days to discuss the costs because I don't want to pay for everything myself. I already called him about this three weeks ago, but he said it had nothing to do with the MSTG (presumably referring to a specific system or component).
If you have to take it to the workshop, you might end up selling the car afterward because the bill is likely to be very high. I realized this myself when I was there, and when I asked if it could be related to the MSTG (a German law), I just got a polite smile and was told...
It has nothing to do with that. We also had the MSTG read out (by 2 friendly people), but they didn't notice that the number was incorrect. So, I would like to thank you again for the tips. I have to say that this forum is really excellent because such mistakes don't happen every day, and you need competent people like the ones here in the forum to help with them.
So, thank you again .

Best regards,
Pedro33