I just got the same code today. Apparently Ford's DPFE sensors have a reputation of going bad regularly. Ford has even told techs not to bother even diagnosing if a P0401, P0402, P1401, or P1402 is stored, and to just replace the DPFE sensor. But the problem could also be that the EGR valve is sticking. The valve itself looks like this:
It's located at the right rear corner of the intake manifold, near the firewall, next to the DPFE sensor.