I have been getting codes P0401 and P0402 continuosly on my 97 Expedition, 5.4L V8. I have removed the EGR valve, confirmed that it is working (holds vacuum, plunger moves up and down, no flow restriction). I have verified that the EGR port in the throttle body is not plugged. I have confirmed that the tube going from the exhaust manifold to EGR is not plugged. I have replaced the EGR DPFE sensor and EGR solenoid to no avail. This thing constantly throws these two codes. What could be going on? The only thing I can think of is that the EGR valve could be sticking after things warm up. I've been through 3 DPFE sensors now and it never fixes the problem for more than a week. Ideas??? Thanks, all.

 

Have you physically removed the throttle body, & upper intake "elbow" to verify that the EGR passages are not blocked?

I just removed & cleaned mine last week. The ports were 100% clogged with hard carbon.

 

Mine are too, I just haven't had a chance to clean them yet. This problem has popped up here recently for those of us who have the older Expeditions. I have been getting a P0401 error for a little while now but haven't noticed it on the forums until the last few months. It isn't a horrible problem to have, but it has cut down on gas mileage and power.

 

Yes, I have removed te entire throttle body and examined the passages. I can easily blow air through the EGR port.

 

It sounds like you've covered all your bases. The only other things I can think of to check for hard carbon deposit build-up, are the 2 rubber hoses that attach to the DPFE sensor. I would also check the metal tube that connects to the EGR valve, to see if there is a carbon deposit build up somewhere in that tube.

Other than that, it sounds like your problem may take an experienced mechanic, who is willing to spend the proper amount of diagnostic time, to figure it out.

Best wishes to you moving forward. Please check back in if & when you get this resolved.

 

DPFE sensor was it - AGAIN! These things are really junk, at least the ones you get at parts stores. I did come up with a way to test them, however. If you remove the sensor and hold it in your hand the same way it is oriented on the vehicle, you'll see three pins. The topmost is the signal output, the middle is the ground, and the bottom is the VREF (+5 V). Carefully attach a +5V DC source between "bottom" pin and "middle" pin, then measure the voltage at "top" pin. When you apply power, the signal (top) pin must immediately go to around 1V. If it does not, or if it creeps up really slowly to 1V, the sensor is bad. If it snaps to 1V, you can further test the sensor by applying some vacuum to either port (doesn't matter, it's a differential sensor) and see the output voltage move. If it moves with vacuum, then it's more than likely OK. If it doesn't move with vacuum, the sensor is bad. The transfer characteristic appears to be fairly steep - that is, not much vacuum will force the output near +5V. Hope this helps other folks. If someone has a more detail transfer characteristic for the sensor, I'd be interested. All in all, this sensor is the weak point in the EGR system and seems to be incredibly poorly designed.

 

would a computer reset clear all your madness seeing you already replaced all the specified parts in your codes.....i would reset before i spent my money....gas is precious. good luck bro