Audi A4 won't start

Hello.

I'm having the following problem with an Audi A4, model year 1999, 1.9 TDI, AVG.

The engine suddenly stopped starting. It starts up, but then immediately dies. It's like the immobilizer isn't disengaging.

The strange thing is that I can't access the engine control unit or the instrument cluster with VAG-COM. All other installed control units can be read.

The indicator instruments in the control panel have recently stopped working, and now the engine suddenly won't start either.

The radio's error memory indicates a communication failure with the display of the dashboard module. Unfortunately, there is no error code listed.

Could it be that if the immobilizer control unit, which is installed in the dashboard module, is broken, I also can't access the engine control unit?

Or there is no power supply. The control lights on the instrument cluster are working, but the display for the onboard computer and the indicator instruments are not functioning.

The indicator light for the immobilizer only works intermittently.

Does anyone happen to have the pin assignments for the control units or the complete wiring diagram?

Thank you.

As long as all the control units are functioning correctly, you should be able to access each one.
Even though the WFS locked the engine control unit, something still had to get in there.

Is it impossible to establish any communication with MSG and AI?

What does it mean that the control light for the WFS (Wavefront Sensor) is only on intermittently?

Disconnect the battery for at least 30 minutes, then try reading the data again and, if necessary, clear any error codes.

Hi,

It rained nicely at night, and is there somewhere where water is pooling?

Best regards, Rainer.

Hello,


I can send you something if I have your address .

Regarding the error: Please check your fuses and the relay for the voltage supply to the engine control unit (which should be located in the engine compartment).



Greetings.

Mati.

sorry, the email is already available.


I sent you something.



Good luck.



Mati.

The engine control unit (ECU) and the immobilizer are communicating via the K-line. This single connection also handles the diagnostics.

If the K-line connection between the MSG (Motor Steuergerät - Motor Control Unit) and the WFS (Wahlschalter Freigabesteuerung - Selector Switch Release Control) is interrupted, the motor would be switched off after 1 second because the WFS could not be reached, and the diagnosis would not function with one of the control units.

What surprises me is that you can't address both devices.

***Activating crystal ball mode:***
One possibility is that a central K-Line distribution block, which may already exist, is slowly deteriorating.
***Crystal ball mode off***

EDIT:

Mati wrote:

Regarding the error: check your fuses and the relay > voltage supply to the engine control unit (which should be located in the engine compartment)

That probably isn't the cause; if it were, the engine would barely start and would shut off after just one second. That sounds more like WFS than MSG.

Thank you for your replies.

I'll try it out sometime, as the car belongs to an acquaintance and isn't in my possession.

I was just looking at the circuit diagram. The diagnostic lead connects to the diagnostic connector via the instrument cluster.

So, would it be possible that if the instrument cluster control unit is defective, I also wouldn't be able to read out the engine control unit?

My suspicion was that the instrument cluster was faulty, but I didn't know if that would also affect the engine control unit's responsiveness.

According to the circuit diagram, it should be like this.

Hello,


Your engine control unit should still be accessible.



Regards,

Mati.

Hello.

The instrument cluster was defective.

Thank you for your contributions.