Originally Posted by Reuel

There has been a lot of talk about the DPFE sensor going bad so I thought I would post a "how to" test the sensor. You will need a volt meter, safety pin and a 3 or 4 ft piece of hose (about 1/4" ID). If you know where the sensor is located skip to the next paragraph. Remove the black plastic cover (3 screws) exposing the throttle body and other fuel related things. Its the cover in the center of your engine that says something like 5.4L or 4.6L on it. Now the DPFE sensor has 2 rubber hoses (about 3/8" dia) coming off the bottom leading in to 2 metal tubes which are leading into a 1" metal EGR pipe coming off the exhaust manifold. On the side of the sensor is a 3-wire connector. This assembly is the DPFE sensor.
Remove the 2 rubber hoses from the bottom of the sensor. Attach a piece of rubber hose to the forward most hole in the sensor. Now carefully take a small safety pin and stick it in behind the top wire parallel to the wire. You do NOT want to pierce the wire, only make contact inside the connector. This top wire is the active feedback signal wire. It will vary from 0-5 volts or so. The middle wire is ground. The bottom wire is 5-6 volts supply. Now the top wire voltage will vary as the pressure between the two holes in the sensor varies. Set your meter to read volts, either turn the key until the accessories are on or start the engine, either way is fine. Now using your mouth apply suction to the hose and you will see the voltage change from near 0 to near 5 if you apply enough suction. The vacuum on the hose should hold your tongue and not leak. If the voltage does not vary or is stuck high or low, the sensor is bad. Do the same thing to the rear port but the voltage difference will be much less, this is the reference port.
If the sensor seems to be working then you can further test the system by doing the following. Attach the hoses to the sensor as normal. Now remove the rubber vacuum hose from the top of the EGR valve diaphragm. With the truck running apply slight vacuum to the EGR valve and this will open the EGR valve. When the valve opens you will see the voltage on the top wire of the DPFE sensor change indicating flow. When the vacuum is applied your truck should stumble or almost stall indicating the EGR valve has opened which it normally does not do at idle. I hope this helps.