Truck has been to the dealer four times for a reading on the DEF fluid sensor, NOT the quality of fluid.

Re-programmed; then new sensor installed; did same again, goes to showing low DEF when actually full and notifies that will go to shut down mode shortly. Did this again just 3 weeks after new sensor. Back to dealer; re-programmed the sensor again. However we have no confidence this is the fix. Planning a long trip it is difficult to know whether we'll make it with this issue hanging over our heads constantly.