Low def but Def thank is full.

I agree. Its the sensor in the tank. Gotta buy the whole tube, wires, sensor assembly. I had a '19 International for a while. Put 3 of them in it. Buy 2 or 3 while ordering.

At one time, International was allowing shops to go into the computer & make some setting changes. The DEF guage would always show empty but at least the truck would run. Just remember to top off the DEF tank everytime you fuel so you wont run out.

Eventually, they were telling everyone, not to let the tank get below 1/2 of a tank. That was causing most of the issues. So when you get a new sensor installed, keep it filled above 1/2 of a tank. That seemed to help.