P1401 code won't go away

My 99 Ranger threw a P1401 code. I replaced the DPFE sensor and was able to drive for 3 days and it threw the code again. I replaced the sensor with another new one, drove for ~150 miles and the CEL came back on again. How do I proceed from here?

[watching & waiting]

I have a similar situation with a code unable to be cleared.

I found that MotorCraft DPFE part lasts years longer than other aftermarket ones. Also, replace its 2 hoses. Other than replacement, it's time to bring out your voltmeter, and start DPFE tests.

Code p1401 means DPFE signal voltage is beyond spec (over 4.0 volts)
when EGR is open (ie, at open throttle, not at idle).

Some reading material for you ...

See
http://www.tomco-inc.com/Tech_Tips/ttt35.pdf
http://www.tomco-inc.com/Tech_Tips/ttt36.pdf

Testing EGR, EGR solenoid, and DPFE sensor:
http://easyautodiagnostics.com/ford_egr_test/ford_egr_valve_1.php

Other Rangers with p1401:
http://therangerstation.com/forums/showthread.php?t=126690

P1401 my fix

I wanted to add my experience, since this code has been hounding me for quite some time. I tried all of the usual fixes first of course.. Replaced the DPFE with one from a junkyard. That didn't work, code came back as soon as I cleared it. Broke down (figuratively, this never actually rendered my truck inoperable. Even when I had the DPFE sensor completely unplugged) and bought a new DPFE sensor, and those things aren't cheap for a 2000 2.5L. I think it set me back over $70. That still didn't fix it. After doing quite a bit more research, I found that the EGR system could get clogged with carbon build-up which has been known to trigger this code. Just to be completely safe, I replaced the EGR valve itself, the EGR tube, and cleaned the ports they connect to really well with carb cleaner. Reset the code, and bam right back on.

I had already visually inspected all of the wires, but since the code itself makes me thing electrical I decided to go a bit further. I very gently tugged on the wires coming out of the harness that plugs into the DPFE sensor. One came out with absolutely no effort, and another came out fairly easily. I suppose this could explain why replacing the DPFE sensor "fixes" the problem temporarily for some people. Handling the harness when unplugging and plugging it in might give the wire just enough contact for a little while.

The parts store wanted over $30 for a new harness, so I went around at a junk yard until I found one in which I could tug all three wires fairly aggressively and they were in there really well. Unplugged the harness, cut off enough wire to splice it to my old wires, and the problem has been fixed ever since for $2. Well, at least I have a whole new EGR system now! I guess that can't be bad for mileage.