Code P0401 Help (1 Viewer)

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So mr scanguage says that i have a Code P0401 with a check engine light. I cleared the code... but have no idea what i should pay attention to.

Help.. whats this mean?
 
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This code means you have a malfunction in your EGR system. There are 4 components to the system plus interconnecting hoses, tubes, and wires. Testing and fixing are covered thoroughly in the archives and probably in the FAQ so see if you can find some threads to help you. Your problem is going to be sifting through the dozens and dozens of related threads but there certainly is not a lack of information on this code.

-B-
 
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That is one of the most common codes. As Beo said, you will find lots of info. To give you a quick summary, most of the problems are related to a faulty EGR modulator, VSV or a leaking or plugged vacuum line or port.
 
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yeah wow.. jsut started searching...

VSV is gonna be the first thing i check/replace
 
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yeah wow.. jsut started searching...

VSV is gonna be the first thing i check/replace
Your strategy should be to be sure you are comfortable with testing each of the components before you start buying parts (BTDT... fed lotsa Dan's dogs.)

The easiest thing to do is to check the hoses going between each of the components. Once you are certain that none are leaking or plugged, then move on to testing components. (Be sure you check the tube that goes through the intake.)

The VSV for EGR is considered by some to be hard to get to. Others that have done it say it is tight, but only a 30 minute job if you don't try to remove the intake as detailed in the FSM.

The EGR modulator is the easiest to R&R and to inspect because it just clips in to a mount. Many guys buy this part (~$50) first but you really should test it before wasting the money if it is good.

The EGR valve is a PITA to remove because of the location, but it is easier than the VSV for EGR. IMHO, it rarely is the cause of the failure but it is probably replaced many times because everyone thinks EGR problem=EGR valve... so they buy a new one. (I cleaned mine twice and bought a new one... didn't fix the problem though.)

The EGR temp sensor is almost NEVER bad. I have only heard of 1 that was replaced by a respected LC shop but we have no way to know if that was the ultimate cure for the problem. However, it is trivial to clean, so pull it out, test it, and clean it... that should make you feel better anyway. :D

Good Luck, and keep us posted. You've got lotsa reading to do. Focus on threads and posts by Raventai if you are feeling overwhelmed with the amount of posts to follow.

-B-
 

Proven

RTFM, STEP 6, POST
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Hello, I found mine was a clogged vacuum line and a frozen VSV. I followed the directions of pulling the intake and I have to say that was a chore. Like Beo said, don't just haul off and start buying parts until you know what caused it. It is very likely that you'll just end up getting more frustrated by doing so. Buying the manual would be a really great first step. The phone number is on here somewhere, or someone that knows it might help you out with it. They aren't cheap, but they are what the factory techs use. Those manuals + this forum = lots of money saved and lessons learned. Understanding how to trouble shoot is mission 1. Period.
 
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P401/P402 are finicky codes fo sho.

Back in June, I cleared 1 code (carbon clogged pass-thru tube) only to have the other code come up one week later :bang: . I decided to add Sea-Foam to my gas just to see if that helps any. Nothing........

at least thats what I thought :doh:

Somewhere between July and October iirc, after living with my check engine light on for years, I noticed my check engine light was gone. its been gone for a few months now. Wifey thinks the bulb just burned out but I didn't tell her it comes on when you turn on the ignition :flipoff2:

Hope it lasts til the next smog check.

btw- dont make this mistake

WET
 
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FWIW: i had the 401 recurring every few days over the course of two weeks in November; and I just reset it with the scanguage and haven't seen it since...

because it is winter and I'm garageless I haven't looked into the condition of the EGR yet. You may just reset it and see what happens? That is one of the key benefits of having a scanguage.
 
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Tripping the P0401 is a relatively complex series of operating variables and it is a 2-trip logic. One of those variables is the intake air temp. If it has been cold where you live it is possible the conditions have not been met and your code is just "waiting" for the temperature to rise.

-B-
 
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I don't consider it "fixed" by any means. But its been over 2500 miles and a temp range of below zero to the 60s F so I'm puzzled. I'll investigate it when things warm up.
 
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There have been several of us that suffered from an intermittent failure in the VSV for EGR. Once it starts failing on a regular basis, you will see how the 2-trip logic works.



-B-
 
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What exactly is the performance loss or reliability issue implied by a 401 code?
Nothing - you can run with it for years. Some would tell you that the EGR cools the cylinders and if it is throwing code - it is not doing it's job. However there plenty of people who have gutted the EGR system entirely without issues.

I reset mine over the period of four years before getting sick of it and finally tearing into it. I would reset it the morning before inspection and it would pass fine.

The two trip logic gets funny. There was a certain section of road I would travel in the old days that would guarantee me a 401 code because how I drove it matched the trip logic as described in the tech sheet Beowulf posted.
 
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What exactly is the performance loss or reliability issue implied by a 401 code?
My biggest concern/fear was that my P0401 MIL would mask another, more serious problem like excessive knocking or cylinder misfires, or O2 sensor malfunction. This was before Scangauge-II (which I still don't have) so checking the code was a pain.

Fixing the P0401 is not rocket science and you can effect a long-term fix. Mine failed at ~95k miles. The P0401 was fixed around ~100k miles. The truck now has ~176k miles. If the EGR system fails again, I will fix it and move on.

-B-
 
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is there one REALLY good P0401 thread to follow... man there are millions of diff threads out there.. not sure where to begin
 

NLXTACY

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The easiest thing to do is to check the hoses going between each of the components. Once you are certain that none are leaking or plugged, then move on to testing components. (Be sure you check the tube that goes through the intake.)
is there one REALLY good P0401 thread to follow... man there are millions of diff threads out there.. not sure where to begin
All I can say is read my thread carefully, laugh, and DO NOT DO what I did :D

https://forum.ih8mud.com/80-series-tech/226972-while-trying-rid-p0401-cel-i-learned-i-am-dumb.html
 
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is there one REALLY good P0401 thread to follow... man there are millions of diff threads out there.. not sure where to begin
... and there is 1 more since you started this one. :frown:

Don't take this the wrong way, but this thread is a perfect example of why we ask members to search before they start yet another new thread on exactly the same thing that has been covered over and over again. If you come up with a situation in your P0401 diagnosis that has not been covered before, *then* start a new thread. We strongly encourage those as we learn more when that happens.

I prefer the threads where Raven contributed. His intermittent VSV problem was solved with excellent testing and diagnosis. However, if you would like to make amends for starting yet another P0401 thread, then you could read all the relevant threads and consolidate the information, the testing, the FSM pages, the images, and everything else into 1 concise thread that would become the definitive way to resolve this code. Gray said he was going to do it a year or so back, but he quit 'Mud instead. (Not a bad thing though... he was hard to get along with. :D)

-B-
 

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