Diesel exhaust fluid sensor failure

Meh, before you freak out too much, research your specific vehicle. My Ram will give me that warning, but it won't go into limp mode until you cycle off your vehicle. So even if it says 200 miles until limp mode, it just means that once you've gone 200 miles, it will still run (theoretically) until you turn off your truck. That at least gets you to a campsite, drop the trailer and to a repair shop.

By the way, I've had that message 2 times in 67,000 miles and cleared it with a code reader and it completely went away.