2016 Prostar abs/tc/ axle load sensor issues ?

What transmission do you have?

 

I would have a good look at the harness where it is run near the transmission for wear. International zip ties the harness to the Allison transmissions and they rub through and create a variety of problems. I don't recall how they route the harness around the Fuller transmissions.
Try connecting a multimeter to one of the j1939 data link pins in the data port and the other to a good ground. The reading should be infinite. Then start moving the harness and see if the meter display start jumping around. on some trucks International ran the wiring harness on the outside of the frame on the left side just behind the steering axle. The harness would wear on the left front ABS modulator valve.
Put the meter on the floor where you can see it and keep poking at the harness.

 

The code is from the display in the instrument cluster?

 

If there is a "A" in the display with the code it is active if there is a "P" it is post or inactive. Do you have the small gauge panel near the centre of the dash? If so is it working?