Just to let you know. I got the same code (P0401) on my 97 4.6l F150, and replaced the DFPE sensor right away. Didn't fix the problem, so I'll be cleaning the EGR ports next. A lot of people have said that this code means a bad DFPE sensor, and it's not always true (actually, it seldom is from what I gather). Now I'm getting a P0302 (#2 misfire) code, which I think might be related. I've replaced the coil packs and the plugs, and will replace the wires next.