Audi A4 2.5 TDI won't start

hello everyone.

Okay, here's the translation:

"I'm having this problem. My Audi started briefly, then shut off again. After several attempts and some time, it ran normally again. I called Audi, and they said the problem was the reading coil. I took it to Audi, and the diagnosis said the key signal was too weak intermittently. The mechanic said it wasn't the reading coil because it wouldn't show up intermittently in the log. Then he disconnected all the connectors, including the engine control unit and the ignition relay (one was slightly oxidized). He didn't find any errors. But then he tried to start the car as usual, and sure enough, it started and then shut off. The connection to the engine control unit was established briefly, then lost. Now the car is at Audi, and they want to replace everything (the combination instrument, engine control unit, etc.). Does anyone have any advice?"to be worth a lot.

Please write in a more structured way (e.g., pay attention to capitalization). Please provide complete details, such as the specific A4 model and the 2.5 TDI engine type.

prutnik wrote:

The car starts, then turns off.

Connection to the engine control unit is established briefly, then lost.

Check the fault memory again after the problem has become persistent. It's likely to be a WFS (likely referring to a specific system or module). I suspect it might be a key (try a spare key), the reading coil, the wiring harness, or the comfort control module (which I consider less likely). I don't think it's the engine control unit or the instrument cluster.

Therefore, I'm excluding the key module (because you have another one), the combination instrument, the engine control unit, and the comfort control module for now. It will likely be just one part, so make sure you only pay for that specific component. Not that they'll end up swapping everything around and charging you for it.

Well, welcome to life. If I understand your description correctly, it sounds like everything is pointing to a faulty reading head. Usually, replacing that will fix the problem... I never agree to wholesale replacements; the risk of exorbitant costs is always a concern. Then it's better to purchase a VAG COM device here in the shop and troubleshoot the error yourself!

Okay, first of all, thank you very much for the help!!!!

Okay, let me summarize again:
-The first error clearly indicates a problem with the reading coil and/or the cable (but the car is running again).
-vag wants to replace the ignition coil, but according to the service log, they say it's not the coil and disassemble everything. They find nothing except that there is no connection to the control unit. They reassemble everything, and the car no longer runs.
- I then requested that they replace the coil anyway, but VAG said no because there is no error message and the key signal is too weak (only occurring sporadically).

According to your statements, I will insist on having the coil and cable replaced again before they replace the combination instrument and control unit.

I work professionally with bus systems and diagnostics, but not in the automotive sector. I'm familiar with the problem of false diagnostic messages. That's why I'm asking again: Could it be that the technician is getting stuck because he's waiting for a specific message? He keeps saying that he needs to see the WFS message, otherwise it can't be the coil.
Has anyone here ever had a similar experience?

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