A couple weeks back I had an odd buzzing sound when I'd bring my 2004 f150 4.6L modular 2wd truck up to 1200rpm from under the hood. Looked around and located the sound was coming from the DPFE located on top of the EGR... I replaced the entire assembly (EGR, DPFE, and EVR) with an aftermarket setup from my local parts store and immediately got a P0405 code after the install. I've checked for vacuum leaks, all good. I've checked the elbow coming from the back of the TB elbow, good, I've removed the TB and TB elbow and cleaned it all ports and the butterfly SPOTLESS with toothbrushes and TB cleaner; and, of course, no busted, leaking or rotting hoses have been found... I've been trying to find the source of my rough idle and it has kinda snow balled into a fair amount of regular maintenance and in depth cleaning, but still can't diagnose the source of this P0405 code.

The next things on my list to try are:
1.) Replace the wiring to the DPFE (particularly since the buzzing noise I originally heard was most likely electrical feedback) or the entire main engine wiring harness if I can find one from a junk yard in good condition.

2. Replace the new aftermarket EGR, DPFR, EVR setup with motorcraft parts (on order now)

Things recently done:
1. Replaced fuel filter
2. Replaced air filter and cleaned MAF
3. Replaced PCV valve (motorcraft)
4. Replaced EGR, DPFE, and EVR
5. Cleaned TB

On a side note I also did an oil change recently and noticed only 4 3/4 at oil came out after 10k from my previous change which was (supposedly) done with 6qt of Mobile 1... seems like a lot of loss but not impossible. I don't think a faulty oil change is a factor, but it is around the same time I started noticing these issues... oh yea and the wife has been driving it for the past couple years since we moved to a car accident prone area...

 

Did you disconnect the battery to reset the pcm during or after replacing the egr, evr, and dpfe?

 

Bad DPFE from the parts store. I had a 2000 Ford Ranger; I replaced the DPFE with an aftermarket brand, and within 10 minutes, it was throwing a code. Put one in made from FoMoCo, problem solved.

Unfortunately, there's some cheap stuff being made as replacement parts.

 

I did, disconnected the battery and cleaned all the connections with electrical cleaner. After plugging the battery back in I let the engine come to temp with a.c. off, waited a minute, a.c. on for a minute, then 10 mile drive to reset the KAM.

Also after I removed, cleaned, and reassembled the TB I reset the TB position sensor. Per another thread I read to turn the truck on (ignition off) wait for the cluster to calm down, floor the accelerator then let off, turn the truck off, repeat twice.

 

....

 

Sorry I didn't fully read you question. I disconnected the battery after.

 

That's what I'm thinking. Oddly enough the aftermarket setup is more expensive than the OEM motorcraft parts. If it ends up being a bad part that will make for an easy fix. Frustrating having to diagnose new parts.

 

Well turns out the Motorcraft part is actually more expensive... if the local ORielly's would have quoted and ordered the right part, I guess they mistook an EGR valve for a PCV valve... ironically they quoted me about $80 for it though ... I decided to just order the part online, should arrive in a couple days. I'll update after I put it in.

On a side note, my cluster started acting up now too (brake and abs indicator illuminating)... I removed the cluster to check and make there was nothing obviously wrong with it (corrosion on terminals, loose wires, etc.) plus I needed to replace a burnt out bulb anyways... the light went away after I put everything back together, hopefully it'll stay that way, or I might have my excuse to swap my XLT cluster to the FX4 cluster Ive been wanting.

 

So I installed a motorcraft egr module today and unfortunately that didnt fix the issue... and my abs and brake indicators are back on... I think its time to consult the pros on this one... im going to go to an exhaust shop and see if they find any issues before I hit up the stealership.

 

Did you ever find a solution to the code? I also replaced my EGR valve due to a rattling noise from the original EGR. My truck runs fine and doesn't have the rattle noise anymore, but it is giving me the P0405 code.

It doesn't seem to be causing any problems, but it annoying looking down and seeing the check engine light on.

I will probably have to buy a new EGR valve..