Christopher Stone

I've been fighting with this stupid code for months now, so it's time to appeal to those more learned in Fords than me, and see what comes up!

The truck is an 02 F150 4.6l and the code is P0401.

On Monday I pulled the throttle body and elbow off, stripped it, and spent 2 hours cleaning those 2 stupid little ports on the bottom (though they weren't very dirty to start with), but once I was finished, the cleaner was pouring out without a trace of carbon, so I'm certain they aren't clogged. Put everything back together and got the code again...

I tried the vacuum test on the egr valve itself and while the engine slows, it doesn't stumble badly or almost stall, so is my next order of business a new egr valve and see if that does the trick? Again, I did pull everything off and clean those ports, so I don't think there's a blockage there. Or should I be hunting for damaged vacuum lines?

In hindsight, one more question... the egr valve port opening where it attaches to the intake is fairly large, maybe half an inch across or so, but the actual port on the intake on my truck is very small... probably an eight of an inch... normal for these engines or something a bit odd with it? (edit : Gonna have to hit the parts yard tomorrow and strip an f150 and take a look I think... I just found a video showing another throttle body spacer and elbow and that port that is 1/8th on mine is a full half inch on the one in the video... wondering what's going on here.... attempted (poorly) egr delete maybe?../. That would certainly produce an insufficient flow code of the port that is supposed to be a half inch is only 1/8th wide)

Input would be very much appreciated!

white89gt

Get a purge solenoid at the yard. My bet is a bad purge solenoid.

Christopher Stone

Well, maybe solved one problem, but created a couple more (never fails right?). Pulled the EGR valve again and lo and behold there was a restrictor plate over most of the opening... pulled that off, put the valve back on, and changed the MAF because I had another one sitting there that looked to be in better shape than the one on the truck...

Idle is better, less grumpy at stop lights, feels like more power overall, but the p0401 came back along with a brand new p0174.

Changed out the maf again for another one simply because 0174 tends to be related to a bad maf, and you never know with junkyard pulls (may go back to the original yet) and swapped the EGR solenoid because I'm utterly certain there's no restriction now, so we'll see how it goes tomorrow!

MrXLT

EGR could be causing the p0174. Have you checked all related to the operation of the EGR? Next most common to a clogged EGR is failed DPFE sensor. I simply had one of the hoses running to it bust on me sitting in traffic once.

Christopher Stone

Welp, swapped to a different maf and ran all over town today... truck is still learning the idle points again (bit low, but not to the point of stalling at lights then it picks up and recovers).... No trace of the p0174 code this time, so the junkyard pull maf was no good apparently, but the p0401 came back DPFE, EGR itself and vacuum lines are my last choices I guess.... time to go hunting, though at least the EGR is easy to test with a vacuum pump... it either works or not

Jbrew

Replace the DPFE and be done with it.

anolen77

Hey friends. Im trying to get my 01 manual 4.6 to pass emissions inspection in our nations capital. Its throwing the following codes: P0135, P0136, O0401 and P0174. I replaced the intake spacer and gaskets and am prepared to change the upstream oxygen sensor ( bank 1) and DPFE sensor (EGR).
My question is: What should I do first? Can I get away with replacing only the oxygen sensor identified with the code? Might there be another cause for the DPFE/EGR code?
This is a work truck.. Im trying to get her back on the road legally and inexpensively. I appreciate your collective wisdom.
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