VAG-COM: Audi 80 B4 TDI Diagnosis (1993)

Hi.
Before purchasing a diagnostic tool, I'm wondering if the B4 TDI from 1/93 is compatible (with VAG-Com). A B4 TDI from 3/94 could be diagnosed without any problems. However, my B4, which was parked next to it, could only be accessed via the ABS control unit with the same device.

'If anyone has encountered this problem before (and solved it), please help me out...'

Thank you.
Hermann.

According to the repair manuals, even for the "older" B4 TDi models with VAG1551, the engine control unit needs to be read. But as you probably know, when switching to the newer 1Z engines in the B4 (around 01/94), different engine control units were also installed. So, your comparison is not entirely accurate. The older 1Z engine control unit is said to be quite picky...

Hi,
The control unit is capable of diagnostics, but it blocks access for most adapters. The professional adapter with a microcontroller from Ross-Tech can do this (allegedly, I don't have any personal experience with it).

Hmmm, then I probably didn't express myself clearly.
I knew that the control unit was diagnosable using VAG1551, so it's fundamentally possible to do.
Die Frage hätte eher lauten müssen, mit welchen hier angebotenen Interfaces das ebenfalls funktioniert. SSorry.

Regards,
Hermann.

palmstrollo wrote:

Hmm, then I probably didn't express myself clearly. I knew that the control unit was diagnosable using VAG1551, so it's fundamentally possible to do. Die Frage hätte eher lauten müssen, mit welchen hier angebotenen Interfaces das ebenfalls funktioniert. SSorry. Regards, Hermann

Why? I meant the interface offered here, not the VAG tester.

I have a B4 TDI from 6/92 and a self-built diagnostic tool (Adapter version 2.4 from this website). I can also access the engine control unit without problems (read error codes). However, I haven't been able to read any live data values so far.
Greetings, Wolfi.

I already had trouble just establishing the connection... It's Maik's interface, which works perfectly with the B4 starting in 1994. But I'll still try adjusting the potentiometers to see if I can get a connection.
Does the interface offered in the online store (99 EUR; http://shop.dieselschrauber.de/ RS232) work properly with the 'old' ECU?
No one has been able to answer that for me yet.

Regards,
Hermann.

Hello,

Okay, with this one, it should probably work more reliably:
http://shop.dieselschrauber.de/product_info.php/products_id/46
The integrated microcontroller ensures more reliable timing when communicating with diagnostic protocols compared to using Windows I/O functions (adapters without their own intelligence).

Best regards, Rainer.

Hello,

I'd like to revisit this thread, as I'm dealing with this issue again: In my opinion, the problem with communicating with 'older control units' isn't a Windows timing issue. Since the communication happens character by character (each character is acknowledged by the communication partner), and the actual transmission of the characters also happens in hardware on a (from a real-time perspective) 'slow' Windows PC, there shouldn't be any timing problems with the signal shape! Except for the 5bd initialization sequence, which is generated by software but, due to its low frequency, is also relatively insensitive to timing inaccuracies. I'm quite convinced that Windows timing issues are rarely the cause!
For example, the control unit in my 1992 V6 Avant cannot be accessed with VAG Com. Only older diagnostic tools from my automobile club were able to establish a connection. I am convinced that a VAG1551 would work.

Observations of the communication with the control unit revealed that it returns slightly different data during initialization compared to the 'normal' KW1281 initialization sequence.
That's why we're seeing "Too many communication errors," and not because of timing issues!

Perhaps someone else has dealt with this issue: I've noticed that after being "woken up" (using command 0x01 with 5bd), the controller reports back with 0x55 0x01 0x8A 0x0F. This is one byte (0x0F) more than usual. After acknowledging 0x0F with 0xF0, it sends 0x01 and then nothing more, but it doesn't provide the expected STG ID block, which is what STGs typically do, and what VAG Com expects. This then leads to a communication breakdown with VAG Com and the "communication errors."

Best regards.
Michael.

I don't think you'll get a specific answer here. Most people here aren't that knowledgeable about it, and those who do know something probably won't readily share that information.

VAG-COM works very well with a V6 engine like yours; I've used it myself and haven't had any problems. The question is, which version and with what hardware did you test?

It's a bit odd to bring up a topic from 2004 just to philosophize about the protocol process, isn't it?

The fact is, as Sebastian already mentioned: it works with VAG-COM (unless you're buying some cheap, unreliable hardware from an online marketplace with outdated software).