So in my emailing with FCCC some early 2018.5 chassis, usually a 2017 build date, the water lines from the engine to the DEF heater got installed reversed. With the heater hoses routed backwards it can cause it to over heat the in tank sensor and damage it. The code seems to be come up when the Outside temperatures are up. After the RV sits and coolant cools down, it seems the code goes inactive. What kind of temperatures are you driving in? I suggest contacting FCCC at
fcccservice@daimler.com or call 800-FTL-HELP