I have a 2011 Winnebago Tour on a 42' XC-L chassis with a 400 ISL Cummins. I have had the problem of "low coolant sensor" with this vehicle since new. Under warranty, I went to Cummins who stated the motor required "burping" and then added an additional 2 gallons of antifreeze. That was back in 2012. To date, I have an intermittent problem of the "low coolant sensor" light coming on, usually while climbing a grade. It's not always easy to immediately pull over to a safe place so a couple of times the motor has de-rated, "check engine light" comes on and stopped me right in the middle of the road. Because of this problem, I check my surge tank level before every daily trip - always finding it at the full level. When the problem occurs, I have found that turning off the motor, letting it set for 10 seconds or so, and then restarting, resets the computer and I have generally been successful in continuing - sometimes for 100 yards and sometimes without interruption throughout the rest of the trip.
I am going to try the following:
1. Put as much antifreeze in the surge tank as it will hold (it makes sense in the fact that my experience is occurring mostly while climbing grades thereby tipping the fluid in the surge tank below the sensor)
2. Locate and clean the sensor wire connectors paying special attention to the ground connection(s).
3. If the above is unsuccessful, replace the sensor.
4. If all else fails - dynamite!