what is P1406

Make sure that the hoses on the DPFE sensor are in thier right positions, and they are not damaged. The hoses are different sizes, but they can be reversed.If the hoses are OK, then the sensor has probably failed. If you have a 4.2 V6, the EGR ports in the lower intake manifold may also be clogged. That will require you to remove the upper plenum, no fun in an F150, and clean the ports