Hello everyone!!! I have a 2016 Nissan Titan XD SV. I recently had the “DEF Error” pop up on the screen and i had two other mechanics diagnose a bad NOX sensor on the front of the exhaust. I then brought it to Nissan for a final diagnosis and an attempt to get it covered under warranty and it has been there for a few days and they just called and said that there is something wrong with the DEF and it looks gelled up. They want to continue with the inspection by charging me $800 for new fuel filters to continue their diagnoses. They say that is the only way to continue. Any ideas or help is appreciated.