Audi A4 Immobilizer Control Unit

Recently, I had a problem with an A4 where the immobilizer warning light was flashing. The stored error code in the MSTG (Engine Control Module) was: "Engine Control Module locked." The entry in the immobilizer control module (STG) was: "1177 Communication between MSTG and immobilizer missing." I then adapted the control modules to each other using VAG 1551. I entered "25" for the immobilizer control module, then "10" for the adaptation number, entered "00", and confirmed with "Q". I turned the ignition off and on again and then tried to start the car.
PS: I'm talking about the A4 model that doesn't yet have the speed limiter integrated into the instrument cluster.

As long as there is no communication between the Motor SG and the WFS SG, no adjustments are possible. Possible causes for this include:

* Interruption in the 'W' line between the SG units.

* The WFS SG is not configured with the correct baud rate that the motor SG requires.

-Uwe-

Are all the errors gone now?
I can tell you that the cable connecting the ignition coil to the immobilizer often breaks, especially in the A4 model. It seems that the cable becomes brittle quickly due to the steering wheel adjustment.
The problem is that the car doesn't always start immediately, or sometimes it stalls right after starting. Usually, there are no error codes stored, except sometimes it shows 'Engine Control Unit locked (ECU)'.
Did your A4 start and the light suddenly began to blink?

"You're right about the cable, but it's not brittle; the problem is the poor contact at the cable connectors on both the reading coil and the engine control unit (ECU) of the immobilizer. I had to resolder them (it's a real pain), and the car started running again."
PS: I experienced this problem with another A4 before!

"Because I travel frequently to Eastern countries, my B5 from 1996 with the AFN engine is quite vulnerable. I already have a power cut-off switch, but I would now like to either cut the wire to the reading coil or the wire between the engine control unit with a switch. This is because there was an attempted theft a few days ago, and nothing was actually stolen from the car, but it seems they were targeting the car. Perhaps my existing switch helped prevent the theft."

What happens if you try to start the engine without the control unit (ECU) of the water pump system (WFS) connected, i.e., with the cables disconnected? Obviously, it won't start. The question is, what happens when you reconnect it? Will the engine ECU be permanently locked, or will it function normally again afterwards?

If you plug the cable back in before turning on the ignition, there shouldn't be any problems. Otherwise, you'll just get an error message in the error log.