This happened last year, but my experience just might help someone else. I had an Audi A4 B5 which was grounded due to an unexplained (and completely sudden) failure of the Instrument Cluster (IC). The B5 facelift immobiliser is contained in the IC, hence a failure of the IC meant the car wouldn't start as the key couldn't be authenticated and the instruction given to the ECU to start the car.

Car was abandoned for a while as the issue had local mechanics stumped (Siena was helpful with the troubleshooting though). We ruled out immobiliser antenna (contained in the ignition barrel) issues and key issues. The car was unused for months until I had a change of heart (she's probably the most pristine facelift B5 in Naija) and attacked the problem.

To verify that the immo was without a doubt the problem, I decided to do an immo delete on the ECU; remember immo in IC authenticates the key, then instructs the ECU to allow the car to start. The immo delete will remove the immobiliser reference in the ECU, thus the ECU wouldn't "look" for the instruction from the IC to start the car. nefariousmotorsports.com provided the knowhow.

Tools for bench-connecting to the ECU:
1. Bosch ME 7.x ECU Bench Harness
2. Multimeter (optional)
3. Battery (the one from your home genset should suffice)
4. Computer
5. Argdub's ME7 program (from nefariousmotorsports.com)
6. Hex Reader (HxD will suffice)
7. VAG COM Cable (KKL 409.1 will suffice)
8. Short length of conducting wire

STEP 1:
Take out the ECU from the car's engine bay. Connect the ECU and the VAG COM cable to the harness, and then connect VAG COM cable to the computer. You will need to put the ECU in bootmode now. Connect the positive crocodile clip of the harness to the positive terminal of the battery (use your multimeter at this stage to ensure you have over 12v). Launch Argdub's ME7 program and type this syntax (but do not execute) "ME.exe --bootmode 95040 --CSpin P4.7-rp4 -b 19200 filename.bin" to read the ECU. Touch one end of the conducting wire to pin 24 as in the picture below.
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Touch the other end of the wire to ground. Connect the negative crocodile clip of the harness to the negative terminal of the battery. Hit enter on the computer to run the program. If you get a result similar to the first picture below, bootmode was not successful and the ECU has not been read.

Try again. You should get something similar to the second below, and your generated .bin file should be in the same location as Argdub's program.

STEP 2:
Open the .bin file using your Hex Editor (HxD). You should have something like the first picture below.

Edit the .bin file at the indicated references to turn the immo off as in the second picture below.

STEP 3:
Write the new file to the ECU using the procedure in STEP 1. Just change "r" in the syntax to "w". Install the ECU, and the car will start instantly.

NOTE: The cluster had to eventually be replaced and mated to the ECU and the key, as a failed cluster means the automatic climate control and a host of other stuff simply won't work. The original .bin file was also written to the ECU to restore the immobiliser functions. But that's a DIY discussion for another day. Also note that I haven't gone into too much detail in some stages due to the sensitivity of the topic.

Have you got a background in engineering or electronics or the sciences?

Love this.

This goes to proof what I have been preaching.

Electronics and Electricals are not accessories to modern day vehicles BUT integral to modern vehicle operation.

And we should expect even more integration and for Electronics and Electricals to take on more functions.

Congratulations!

AutoElectNG:
Have you got a background in engineering or electronics or the sciences?

Love this.

This goes to proof what I have been preaching.

Electronics and Electricals are not accessories to modern day vehicles BUT integral to modern vehicle operation.

And we should expect even more integration and for Electronics and Electricals to take on more functions.

Congratulations!

Thanks! I agree with everything​ you said.

I must confess I do have a background in engineering. Knowing my way around computers also helped a bit.