Volvo VNL Break Demand Sensor
2 identical sensors, one in the dash left from the break pedal. Another one is under the truck on ABS module under passenger side. If you change both sensors and the problem doesn't goo away (after calibration), then replace pig tail under the cab (dirt damages it).
This video shows how to replace the sensor in the cab:
https://m.youtube.com/watch?v=tIHqz0cwHI4
Cable tag E1
Sensor ~ $150
Pig tail ~ $50