I believe that code is related to the DEF system running it's own self test and not the heater. Try this. An onboard test must be commanded using a scan tool. A fluid quality test or a forced REGEN will make the monitor run and the messages should clear and the system should return to normal. Basically, you need to force a fluid quality test using a scan tool.
Try this and let me know if it helps.
Friday, November 8th, 2019 AT 6:15 PM