Hi Michi,
Fortunately, it suddenly started working again, and the preheating light remained off.
I would like to understand how the error is generated, specifically how the control unit detects if the EGR valve is constantly open.
I'll see if I can remove the entire EGR system.
Just today, I discovered that we have an ultrasonic cleaning device at the company. I'm going to verschandeln the AGR first. However, I tend to give up immediately when problems arise

. I really don't feel like tinkering with this thing again.
Best regards,
Jörg