The cursed P0401 EGR Flow Insufficient

[chevyrulez1]

After battling with this for some time, I thought I would post this to hopefully help someone else out, as I struggled to find any information on this problem.

There were a bunch of references on how to check, clean the EGR port, etc. but I have tried every trick in the book and kept getting the check engine light with the same code.
I changed the EGR twice, replaced the MAP sensor, replaced the MAF sensor, checked all over for vacuum leaks, could not seem to make this thing go away.

I pulled the hex head plug from the EGR port and ran coat hangers up in there and did the old "Intake Manifold Cleaner" trick and shot this stuff in the EGR port while revving the engine, but the code kept coming back.

Finally, out of desperation, I pulled the common chamber off and yanked the intake manifold. First of all, let me warn you that this job is terrible. The factory repair manual doesn't make any reference to the variable length intake system on my vehicle, so this left me wondering what all the levers and diaphragm actuator on the back of the intake was. It doesn't even show up on any parts breakdowns, etc. that I have found. In order to get the intake off, you must cut off a 6mm hex key (Allen Wrench) to get the small bolts off the vacuum switch bracket, also there are two bolts on the back of the intake that had little brackets that attached the fuel hoses to the back of the intake also making it impossible to separate the fuel rail from the intake. There is all kinds of little garbage bolted on to the back of the thing that you cannot get to with it in place, and cannot take the intake off until it is removed, so prepare for colorful language while trying to wrestle the thing off.

All in all, I am glad I did remove the intake, because the intake manifold gasket on the drivers side was cracked, and actually came apart when I tried to pull it off the head. I would assume that this is the source of my high short term fuel trims (20 to 40% at times) because it was causing a vacuum leak under the intake that I could not get to. So this should be problem one solved. However, I did find the source of the EGR fault as well (finally).

As it turns out, the port from the EGR goes into the common chamber, and then takes a 90 degree turn and has a pipe that comes straight through the center of the common chamber towards the throttle body. You can see a picture of this here http://user.va.net/~danoakes/MyPictures/IMG_1421.JPG
I had tried to clean this before from the EGR port, but you cannot get to the other end of the tube using this method. When I looked in the Throttle Body end of the tube, sure enough it was packed shut with black carbon. It took a lot of work to get this clear by reaming it out with a wire coat hanger. NOTE** I will clean the inside of the chamber before reinstalling, this thing is nasty.

My advice is this, if you have this code, clean the pipe from the EGR port to the 90 degree turn, and then remove the throttle body. You can reach the other end of the pipe through the throttle body opening in the common chamber to clean the pipe from here back to the back of the common chamber. Here is a picture of the end of the pipe from the throttle body opening.
http://user.va.net/~danoakes/MyPictures/IMG_1422.JPG
My only advice here is to be careful not to damage the throttle body mating surfaces as you are scratching around, as the end of the pipe is slightly lower than the opening. I just hope this will help someone and keep them from having to struggle as much as I did.

[KJK]

After screwing around with the EGR valve itself I discovered the pipe in the intake by accident when I removed the throttle body to clean it well. I used a piece of wire and held a vacuum nozzle by it to suck up the carbon.
I bet my intake gaskets are fubared as well though.