"Insufficient EGR Flow" code P0401 CEL

[Dohc98vteC]

On my 98 Prelude, 150k. From what I have talked Honda techs, they advised to clean the egr valve, which I have done, but no luck. How can you tell if the egr is bad? Also, it has been suggested to remove the intake manifold since carbon is stuck in there causing the code. Anyone have any advice?

 

[brianl703]

The usual test is to start the engine and apply vacuum to the EGR valve. The engine should stall. If it does, the EGR valve is OK. Then the problem is either the vacuum solenoid or the EGR flow sensor.

 

[punisher]

First, I have no idea if you have a vac operated EGR or an electrically actuated one. If vac operated, apply vac to it, verify the pintle opens. With the engine idling, apply vac to the valve, the engine should stumble badly or die. If the engine continues to idle OK, you have clogged EGR passages and they need to be cleaned. If the engine stumbles and dies, look toward a vac problem, or bad EVR.

Electrically operated, no real diag idea on that car.

 

[Merkava_4]

I'm thinking it is probably electrically operated; which means you would plug a scanner (not a code scanner) into the DTC scanner port, and the ECM's information will be displayed on the scanner. It will display a % of EGR opening along with all the other engine parameters.

If you don't have a scanner, you can hook up a volt meter to the EGR's connecter and it will tell you if you're at least getting a reference voltage to the EGR valve; which is usually about 5 volts. That will at least tell you if it's powered up, but it won't tell you if it's opening.

You could also take a shot in the dark by clearing the code and installing a new EGR valve and seeing if the code reappears; if it doesn't, you're done.

 

[punisher]

You will get a different code if there is any electrical problem with the EGR circuit.

 

[wavinwayne]

Quote:

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Dohc98vteC wrote:
...Also, it has been suggested to remove the intake manifold since carbon is stuck in there causing the code. Anyone have any advice?

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I have first-hand experience with this problem, albeit in a much different engine. The EGR passages in the upper intake/throttle body of my Expedition were completely clogged with hard black carbon deposits, and I was getting this same code. I removed the part that was clogged, and scraped the carbon deposits out with a .223 caliber rifle bore cleaning brush.

If you do this, try to NOT use any type of solvents. I used Seafoam spray & B-12 spray, in an attempt to break the carbon deposits loose. All it did was make a huge greasy black mess. I think the carbon would have broken free much easier, had they been dry when I began scraping them out. Also, a good set of basic dental instruments would have made the scraping job easier, in the hard to reach nooks & crannies. After I bolted it all back together, with new gaskets, and installed a new Motorcraft PCV valve, the problem went away & has not returned. It was a pleasureable afternoon project; not difficult at all. I have pics somewhere. Good luck solving your problem.

 

[wavinwayne]

Found the pics; Here is what the part I was talking about looked like before & after I cleaned the carbon out.

Before

After

 

[Dohc98vteC]

Thanks for the pics, I posted on another forum and found out that the EGR ports have caps can be drilled out and clean inside the manifold without having to remove the it, which is great news. But the passages appear pretty small, so the rifle brush seems like a great tool to get in there, and my 1 hp Shopvac will get all the loose deposits like nobody's business. I was thinking about spraying it all with throttle body cleaner, but I will not after reading waynes post.