Soot Mass Negative: Audi A3 P8 2.0 TDI CR

Year of construction: 2010.

Every 3 to 4 weeks, a "Diesel Particulate Filter" warning light illuminates on the instrument panel. It usually disappears after a longer drive. Since this has been happening more frequently, I decided to investigate.
No error codes are present, but the measured soot mass is negative. I installed a new differential pressure sensor and calibrated it using the basic settings. The measured soot mass is still negative.
The instructions state that you can program it using "Coding 2." However, I can't click on that field in the vehicle's settings.

Does anyone have any ideas?
Thank you very much.

Hello,

As a customer who purchased your vehicle from a dealership, you are unfortunately not entitled to support. Diagnostic-related inquiries are exclusively reserved for our customers who have had diesel engine work performed.

The following option is available:
Vehicle Diagnostics Support Key

Best regards, Rainer.