Ok I've searched dozens of times and always found a- just unhook everything and clean it out and it's fixed answer. I'm not a huge mechanical person so this intimidated me. I finally after popping the hood and staring at the engine for 10 minutes then giving up, decided to just dive in. Idid this yesterday so I miss some steps and all edit in some pictures later.

1) disconnect negative battery terminal.
2) remove your intake, along with all electrical connections and hoses.
3) you now see your TB with some wires and hoses still hooked up. I unhooked the TPS (top right of your Throttle body), unhooked the throttle cable. Unbolt the hose from the side of the fuel pressure regulator that runs to your brake booster. This is on the right hand side near the firewall. Unbolt the fuel pressure regulator.
4) unbolt the TB- 4 screws in front, I left the cruise cable hooked up and just set this on the side out of the way. Now you're getting to the meat. I went and unhooked all the hoses I could reach. I don't know if you have to or not, but in the cab passenger side behind the kick panel there's an electrical connection you can disconnect to relive pressure in the fuel system. I did this before disconnecting the fuel line in.
5) You will now be able to see 2 bolts on the left hand side pretty easy, and there are also 2 on the right. All 8mm. Take your time, undo these and don't drop them. The back right one was the toughest for me but my smallest ratchet with the smalles extension fit just right. Once you get it turned about 2 turns you can back it out the rest of the way by hand. I still had one hose in the back to unhook once I got it all unbolted.
6) look inside and you will probably see the 2 growths of carbon. I started picking away at it. After working on it for about 10 minutes I thought I had made a dent, not even close. I kept picking and then started spraing with carb cleaner, and pick some more. spray and pick, repeat for about 20 minutes. I used an old toothbrush down the EGR input hole and it fit perfect, twisting as I went down it cleaned out alot. Eventually you'll be able to actually see through the 2 small ports.
7) clean everything up good and use compressed air to dry up. Time to bolt everything back up. Don't forget your gaskets, because then you just have to undo the bolts again (not that I did this or anything)! Now I triple checked and made sure there were no loose hoses, or electrical connections. Make sure the throttle cable moves smooth. Plug back in the connection on the passenger kick panel. Hook up your negative battery cable. I went turned the keep to on, but didn't start yet. I let the fuel pump prime and made sure there were no leaks there. Fire her up. Runs much smoother now.


I took the truck on a short drive- no more rocks in the engine under acceleration, and no more CEL. The only problem I do have is the gas pedal/throttle cable is sticking a little when I very first press on it, so I need to go recheck that.

key words: EGR, P0401, CEL, insufficient flow, fix, how-to, how to

 

I have been considering the same procedure for a while now. Guess I'm still a little chicken. Not a very good mechanic so I'm a little gunshy. Your steps sounded pretty easy though. I might get brave next weekend, what the hell, its only my truck right?

 

I was the same way, but it was really pretty easy. I'm not mechanicaly inclined so you should be fine. Just take your time and remember to double check when you're done.

 

My PO401 was easy to fix on my 5.4. It was a bad DPFE. i just replaced it

 

P401, I coverd it before.
Here it is again.
It is the insufficient flow code.
The test is done after the EGR has been operated from other routines to try and eliminate other faults first. The 401 test is tried 2 driving cycles before the CEL lamp is lighted for failure so it is not an immediate fault triggering event. It normally does not alter the engine's running ability because it is 'only' an emmissions test.
How it's done.
The PCM commands the EGR to open about 10% flow.
The DPFE measures for an expected flow drop accross an orfice in the large pipe from the exhaust manifold to the EGR and into the Intake manifold.
The DPFE stands off the main pipe on small pipes with hoses connection off each side of an internal orfice in the large pipe. It measures the drop accross the orfice and reports it to the PCM for a match, within tolerence, to a table in the program.
How to test;
Remove the DPFE, start engine and feel for exhaust from each small tube as a test for an open orfice. Clean as needed.
To test the EGR, remove it's vacuuum hose with the engine running and apply vacuum. Good test will make the engine run rough indicating the EGR can operate, and the path for the exhaust is open.
Faults:
The EGR, the EVR, the path is plugged, the DPFE is defective, it's hoses are faulty, electrical plugs or anything that interferes with these operations.
The testing needs to sectionalize the areas to find where the fault is and can be more than one fault at the same time on high milage engines.
Note the EVR is the PCM operated solenoid that gates vacuum to the EGR from full intake manifold vacuum.
As Charlie Chan would say, USE HEAD PLEASE AND THINK! Save precious air, effort, time and money to get the pleasure of success.

 

Maybe I should have posted this before- my mechanic supposedly tested and replaced EGR/DPFE and all ines previous, and code was still there. The only thing not done was cleaning the ports. Now that's done and 2 days no light until, today at lunch the code is back so time to retest the EGR/DPFE.

 

After the engine is cut off the solenoid before the EGR is rattling until all pressure is equalized, is it supposed to do that?