You can look up the code HERE. Essentially it says that the P1400 code is caused by either a bad DPFE sensor or there is a problem with the DPFE wiring harness (grounded) somewhere in the circuit. So you'll want to check the harness and connector for any signs of distress.

However, I've also heard that a P1400 might also be set when the PCM reads a lower voltage than expected, and not necessarily just an out-of-range condition. In such cases a P401 code would be anticipated as well, but I suppose you never know. As such, it might be wise for you to check over the entire EGR system to the best of your ability, using the tips and suggestions put forth in this thread:

https://www.ford-trucks.com/forums/1...ufficient.html

HERE is a summary of the Ford EGR/DPFE system for further reference.