CEL code 1400

I was changing the plugs in my parents taurus (99 3.0L) a few days ago, and since then it has started to run alot rougher. I have checked the gap on all of them, but now I am getting Code 1400 (Differential Pressure Feedback Electronic Sensor circuit Low Voltage). I have NO IDEA what this means. Any help would be great. Also, if it is related the EGR valve is running on borrowed time allready.

That sensor is a known troublemaker,, your engine 12v or 24v??? I think it's located near the top left-side of the upper intake manifold,, I think there's two vacuum hoses and an electrical connector, price is probably around 50 bucks, just guessing... you can always pull your egr valve off, make sure it isn't all carboned up,,, make sure all your wires and hoses are still in place with that sensor, in case you knocked something off while doing plugs. My experience is that almost all the time the sensor has malfunctioned, barring disconnected or corroded items, not only with that piece, but most... Ford systems have been reliable for me..

Voltage return on the Sensor is below its expected range.
DPFE sensor is most likely faulty or broken.

Or the wires or the hoses might have been knocked loose when the rear plugs were changed.

Speaking of the EGR Valve, is there an easy way to get it off? I have busted alot os sockets and it still won't budge.

The Differential Pressure Feedback sensor will also generate a code 1401 which means the voltage return is above what is expected. Just thought I'd throw that one in there too. I replaced mine and code is gone.