A friend is getting this code on her diesel F250. Sounds like either the DEF sensor or the wire/harness to the sensor is the issue. This is the sensor which turns on a glow plug for the DEF when it gets cold out (not an issue in Dallas ATM).
Not wanting to waste money at the dealer, is this an easy to diagnose/fix sort of thing?
Recommendations?
Hank,
What year and how many miles are on her truck?
I ask so that we can eliminate whether or not it may be covered under the federal emissions warranty.
2014 model year
88,400 miles
From what I just read, she missed the 80,000 cutoff 
Hank,
You /your friend may want to call your local Ford dealer and ask about the TSB that Ford released on that sensor to see if that truck falls under it - it may be covered under the TSB(technical service bulletin)
Thanks, Tom. I just let her know.