Audi 80 B4: Engine Control Unit (ECU) Not Responding

Hi,

I tried to access the engine control unit using the original VAG1551 and a 2x2 adapter (from an online store). The ABS control unit worked immediately, but the Mtsg (likely referring to a specific module) did not. The display shows the message "Control unit does not respond!"

Although it is possible to communicate with the ABS control unit, could the issue be related to the wiring connection?

- Or could it be due to the modified software (chip tuning) of the engine control unit?

Sure, here is the translation of the text from German to English:

"Further notes:"
The engine starts and runs perfectly fine, so the Mtsg (presumably a component) probably isn't directly broken, or at least I can't imagine it being the cause.
The VAG1551 combined with the 2x2 adapter worked perfectly in an Audi 80 B4 with a 2.0L ABK engine, specifically for the engine control unit and ABS control unit.

How should I proceed, or what should I try?
Thank you in advance for your help.

The 1Z control units have been causing real problems since then. In some cases, it is impossible to establish a connection using a conventional interface; it only works with a smart interface (HEX-COM/USB).

Of course, a prerequisite is that the chip tuning has not corrupted the engine control unit's software, making it impossible to perform a diagnostic check.

I'm already familiar with the stories about the 1Z control unit; don't worry. They often mention that this control unit is quite sensitive to the interface.

In my case, I use the original VAG 1551, and that should definitely work , so I don't have any interface problems.

Okay, so it seems like, based on Jörg's response, that just because the ABS control unit can be accessed, it doesn't necessarily mean that the engine control unit can be accessed. So, I should be looking for my problem along the K-line or L-line, from the diagnostic connector to the control unit?
Good that's been clarified.
Regarding the second point:
Can a modified software, achieved through chip tuning, cause the engine control unit (ECU) to become inaccessible ("...not responding!")?
I mean not an error in the fault memory, like "control unit defective" or some other nonsense. I haven't even gotten that far yet.

faz wrote:

... Regarding the second point: Can a modified software, achieved through chip tuning, cause the engine control unit (ECU) to become inaccessible ("...not responding!")? I mean not an error in the fault memory, like "control unit defective" or some other nonsense. I haven't even gotten that far yet.

Hi,

It's possible, who knows what might have been altered in those EPROMs. Couldn't you simply plug the original EPROMs back in to test it?
Otherwise, the only other thing I can think of is to check all the cables and connectors that run through the K/L line.

Best regards, Rainer.

I read somewhere that, in some cases with 80s models, the engine control unit could only be diagnosed from the engine compartment. But I can't remember where I read that... Alzheimer's is kicking in.


Use a pass-through diagnostic tool and check the K and L lines all the way to the motor control unit using the diagnostic connectors. I think the problem might be located there. The original diagnostic tool should actually work.
If, unexpectedly, you experience a crash, your graphics card might be the culprit.

The B4 has its two diagnostic connectors in the fuse box, which is located in the water reservoir under the windshield.

Okay, then I'll try to figure this out using a multimeter. I still have the original chips. If the connections seem right, I might try plugging them in just to see what happens. We'll see what it is then. Next weekend, I'll take a closer look at it.

Thank you for your help!

Hi, you might want to try the following before you start disassembling everything, because I know there were issues with the 1Z in the B4 related to the connections to the control unit when a radio is installed. Just try removing the car radio and then try reading the error codes again. Best regards, Jürgen.

@Klemmi

What is the background of the radio in this case? I can't think of anything specific right now. I mean, it's a normal radio, completely without CAN-Bus and so on (given the year of manufacture ).

What is the background of the radio in this case? I can't think of anything specific right now.

Oh guys, why don't you get used to doing a quick search first. This forum shouldn't turn into a chat forum like Motor-Talk, where everyone first asks a question and then thinks or searches.

Regards,
Private.

I checked the K and L lines from the diagnostic connector to the control unit. There is continuity. There is also no short circuit to ground or anything else.
Just for the record.
According to the wiring diagrams, the K and L lines run directly from the diagnostic connector to the control unit. There are no additional lines to the radio or anything else. However, I will still remove the radio next weekend and then try swapping the chips in the control unit as a test.

For the sake of completeness: Control unit VAG 8A0 907 401 B or Bosch 0 281 001 185.

First of all, it had absolutely nothing to do with the radio. In my opinion, it probably can't have anything to do with it, since there's no CAN bus system here at all (it's a really old device).

Secondly, the problem was not related to the software of the engine control unit.

It was actually due to the VAG 1551! With that specific device in this workshop, no connection to the control unit was possible. With a 1551 from another workshop, it worked!

Who would ever think that the original devices might not be compatible...?

The B4 has its 2x2 diagnostic connectors in the fuse box, which is located in the water reservoir under the windshield.

There are different software versions (on the plug-in card) available for the 1551/52.
and these individual software versions are not identical, logically .
Some functions were added, but others were also removed.

1551 in speech is not the same as 1551 .