Broke open the DPFE sensor that I removed. It is just a common 
differential electronic (piezo...) pressure sensor with +DC, ground and 
signal terminals. There are 2 ports to provide the differential signals. 
One of the ports had a small (3/16" dia. x 1/8" long) foam filter. The 
filter was saturated with water (or similar liquid), probably from 
condensation. The symptom  that was looked for, check at rest voltage, 
should be around 0.6 VDC, exercise, by manually opening EGR valve 
briefly, voltage should increase, say > 5VDC, allow system to go back to 
rest mode quickly. If the voltage took more than a second or two, 
replace the sensor. Apparently the liquid needs to be pulled out of the 
foam, and that slows response. The vehicle has 78,000 miles in 7 years 
for this fault to be apparent. The gasoline mileage is back up, which 
tells me, this has failed for about a year, but, just recently set the 
check engine light.

The replacement Ford part is different, in that it does have an ambient 
pressure vent on the top side of the PCB and is larger case overall, 
where the original sensor had no vent.
> Carl Denk wrote:
>   
>> Had a 2002 Mercury Cougar with a 2.5L. V-6 that was getting less than
>> great fuel mileage (27 vs. 32 MPG highway) for some time, thought it was
>> the alcohol in the gasoline, since that came about the same time to the
>> area. Recently got the check engine light, scanned with the AutoXray
>> Ezlink scanner I have had for some years, replaced the EGR valve, but
>> the light and P0401 code came back in a week. Tracked the problem down
>> to a sticky DPFE (Differential pressure feedback EGR) sensor, which I
>> replaced. The fuel mileage came back to what we have known. Anyone with
>> a 2000 - 2003 Ford should check this out.
>
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