See TDR issue 114 and 115, The Rest of the Story for some additional info on P207F fault. You probably need Alfa OBD or a good scanner to see what the DEF concentration is that the ECM is seeing.
What I’ve read so far is people getting diesel in their DEF tank and since diesel floats on DEF it took them running the DEF level low for the problem to occur. That’s crazy and a scary thought. I’ve been typically filling my DEF when I hit half tank as I drive a lot and I’m not worried about it getting old. It was at a quarter tank when I got the code. I’m very careful at the pump and haven’t let any body run my truck. Drove it pretty far this weekend and so far so good!
I’ll keep reading to see what other information I find in issues 114 & 115