So I finally found a setup that would read my CEL. Turns out is's a P21DD. This code is a DEF tank heater open circuit that's detected by low conductance in the heater. Has anyone else experienced this? Is this covered under warranty considering I just turned 37K miles? I'm thinking it's a loose or bad plug because it's been way above 12 degrees around here for a while and the CEL light has only been on for a couple of weeks. Suggestions?