Insufficient EGR Flow

On my 2001 Ford F150 4.2L Truck I had a “Service Engine Soon” Light. The diagnostic code was P0401.
Insufficient EGR flow. I removed & checked the EGR valve with a vacuum source. The valve was good.
I also checked for carbon blockage. That was ok. I decided to put a vacuum gauge in the vacuum supply line to the EGR valve to see if was getting vacuum as it was supposed to. Here is what happened. When the truck was first driven the vacuum gauge read about 6” hg. When the truck reached operating temperature, the gauge read 0. No vacuum. Any suggestions as to what the problem might be.

Call your dealer...the check engine light and codes in the 4.2s had a few glitches that aren't easily fixed by the untrained eye.

It wasn't worthy of recall status, but i know of a few trucks that had that problem.

well, there are a couple of things. It is not a glitch, this a a major vacume leak and a kinked vacume line. Does your dash instruments work right, or is it stuck on defrost?

well, there are a couple of things. It is not a glitch, this a a major vacume leak and a kinked vacume line. Does your dash instruments work right, or is it stuck on defrost?


Replaced the DPFEGR Sensor. So far so good

Got it from Ford Dealer
Part No. 4U7Z-9J460-AA for $29.78 +tax

There is another sensor that cost $85 but the
electrical connector won't fit my truck.
Don't know why the price difference, but it sure pays
to investigate.

Hello Everyone! This is my first time posting here and I hope that my input helps.

I have a '02 Expedition with a 4.6L with less than 40k miles on it and I had a similar experience last week. My check engine light came on and I did the same thing by hooking up an OBDII meter and found that I had two errors. The first said (or words to this effect) that my egr system didn't have enough air flowl, and the second error said that my egr system had too much air flow. With that, I reset the faults and drove home to take my egr valve off to check it out. The valve was fine, but I sprayed a little WD-40 into it just for good measure and I put it back together. The next day, the light came on again, and so I read through the manual and it seemed that I had three units to consider: (the terminology may not be exact) the vacuum generator/regulator, the egr valve, or the air flow sensor. The resistance reading from the vaccuum regulator checked out fine, so the next logical part to swap was the oxygen flow sensor. And hey, what do you know? After swapping it out (btw, the original was plastic and so is the replacement), We took a short trip and logged over 100 miles and no service engine light came on! The 4U7Z-9J460-AA sensor seems to be what failed. (Does anyone have much experience with these sensors, and should they fail so soon?)

But, I bought my sensor from the Ford dealer because I wasn't sure to trust the other auto parts stores for exact compatability. Btw, after taxes, I paid about $70.00 at the dealer, and I'm wondering if I would have realized a significant greater savings by purchasing at AutoZone or some other autoparts store?

Oh yeah, if I misnamed something or something here needs correcting, please let me know. I'm always happy to learn something new!

I hope that this lends a little more experience on this issue.