P0401 code that will not go away! (03 Honda Civic)

[Matt Brandsema]

So I replaced the head gasket on this car about a month or so ago. Shortly after I finished the head job, I get this P0401 code (Insufficient EGR Flow). So I removed the intake and cleaned out the EGR passages on the plate attached to the intake. I didn’t do anything for the head side because the head was thoroughly cleaned at the machine shop when I brought it in to be machined, so it all looked good. Put everything back together (with a new intake gasket) and I still get the P0401 code.

So then, on a whim, I replaced the EGR valve, and I STILL have the code! What else is there? Since it happened right after the head job, I am thinking maybe I forgot to attach something??? I don’t know where the EGR connects to the exhaust but that is the only thing I don’t think I have checked. (I think it may do so through passage ways in the head).

So then I thought that maybe the intake wasn’t torqued down carefully enough. So I sprayed carb cleaner (as best as a could, so I could only get to the top side) all around the intake and got NO change in RPM. So it is fine.

Can anyone help me out here??

Topic

[Rob]

MAP sensors are really comman to give you egr errors in fords I dont know if that is the problem I would first do a vacuum check to make sureyou dont have a vacuum leak first… chck the PCV value and see if that is cousing any peoblem I dout it is it but give it a check… Im thinking you have a leak or a bad map secors you can see what others say but I would check that… you can also check the egr silinoid and that might be gettinfg stuck

[Matt Brandsema]

I finally got around to the shop today. I hooked up my scan tool and looked at the data from the MAP sensor, and it seemed to make sense, but I don’t know much experience looking at MAP sensor data to compare to.

I hooked up a vacuum gauge and measured the vacuum at idle. It was about 18 inHg. I slowly revved it up and the vacuum went up to like 25. When I let it go back to idle the vacuum was at 22 inHg. So I do not think I have any kind of vacuum leak, especially one that would cause a code to be thrown.

I already replaced the EGR valve and it didn’t fix the problem. I am at a loss!

EDIT:
I am starting to think that maybe it is something crazy like, chips from the machine shop stuck in the EGR passageways in the head. I feel like the EGR system is simple, and I have checked everything except for these internal passage ways.

[Richard Kirshy]

Just a thought …
Did you inspect the EGR tube for damage or cracks?
Is it seated correctly in to the EGR valve?
Is the bolt holding the tube threaded correctly.?

[Matt Brandsema]

[quote=”nightflyr” post=178699]Just a thought …
Did you inspect the EGR tube for damage or cracks?
Is it seated correctly in to the EGR valve?
Is the bolt holding the tube threaded correctly.?[/quote]

So that’s the thing, I do not think this EGR valve has any kind of tubes. Here is a picture of it.

The EGR valve bolts directly to a casting on the side of the head. In the casting there are two internal passage ways that go into the head. The passage ways are pretty large, and when I had the EGR valve off, it didn’t seem like they were gunked up at all. But maybe what I need to do is remove this casting from the head. That is a lot of work though and I would like to avoid doing work if I don’t need to.

Here is a picture of the side of the head with the casting removed that I found online. Here you can see some of the internal passage ways. The one big square one is for coolant I believe, and the two flatter ones are for the EGR.

Here is a picture from alldata. You can see the EGR bolted to the casting I was talking about (which is labeled as “water passage”).

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• HondaEngine1.jpg
• HondaEngine2.gif
• RO1.jpg

[Its me]

There are air intake passages on the intake manifold that get clogged. Remove the plastic piece from the intake manifold and take a look in there (part #7) on the side that has the gasket…

Good luck

-Karl

Attachments:

• intake-manifold-2514973.png

[Richard Kirshy]

As i said ..it was a thought..

You can look at this ..
Perhaps the fix is listed.

A code P0401 most likely means one or more of the following has happened:
The DPFE (differential pressure feedback EGR) sensor is faulty and needs to be replaced
There is a blockage in the EGR (tube), most likely carbon buildup The EGR valve is faulty
The EGR valve may not be opening due to a lack of vaccuum

Possible Solutions In fixing this code,
it is quite common for people to just replace the EGR valve only to have the OBD code return.
The EGR valve is not always the culprit.
Use a vacuum pump and pull the EGR valve open while monitoring engine RPM’s & DPFE voltage.
There should be a noticable difference in RPM’s with the EGR open
Clean out the EGR valve and/or tubing to remove deposits
Check the voltage at the DPFE, compare to specified values (refer to a repair manual for your specific model)
Replace the DPFE sensor (with a good quality / OEM one)
Replace the EGR valve

[Matt Brandsema]

Can’t be a bad sensor because all of the electronics came with the new EGR solenoid, as I think it is all built into one assembly (The valve has like 5 or 6 pins on it).

My EGR solenoid is electronic, not vacuum controlled.

I think what I will do is energize the solenoid at idle and see if I get a change in RPM.

[Rick Cropper]

Just remove the valve and run the engine with it off. You should have exhaust on the valve inlet side and vacuum (suction) on the discharge side. It’s probably just still plugged up somewhere.

Rick

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