Mercedes W203 c200cdi glow plug problem?

Hello Laute, I have the following problem: I did a vehicle scan and it shows me a short circuit on cylinders 2 and 3. I replaced the 4 glow plugs a few weeks ago, and the error is still there. I thought, OK, it could be that the glow plug control unit is also defective. I replaced it today, drove around, did the scan, and of course deleted the errors, and lo and behold, the same error was there as before.

Does anyone have any idea what could be or where the problem lies?

Thank you