Hey guys,

I'm working on a '00 Monte Carlo, 3.4L ATX. The car is throwing a code (going by memory here), p0401. EGR Flow Insufficient.

I went ahead and took off the EGR valve, cleaned it up with throttle body cleaner, cleaned up the throttle body itself with the cleaner and put things back together. I cleared the code and shortly after it came back.

I was just wondering if any of you had experience with this particular CEL code... suggestions? Tomorrow I plan on taking the valve off and getting into the EGR tube itself to see if there is some sort of obstruction there.

I did a search and came up with a few possibilities but would like any feedback you might have to offer.

Thanks for reading,
Michael

 

Going off of memory but its probably a linear type EGR valve. Meaning its not vacuum operated at all.. its all done by the ECM. The pintle might be stuck shut and cleaning it out doesn't always work.. best bet is to replace with a quality AC-Delco unit. But before you replace it try this: Pull the vacuum to the MAP sensor and check for blockage .. if not clean the MAP sensor with an electrical motor type cleaner ( Doesn't leave a residue ) and reset the PCM by unhooking the battery. Apparently around these years the map sensor would run an EGR test upon decel and if there isn't sufficient flow it would set a code... but a bad/dirty map sensor or plugged map vacuum could set this code.. From what i read its common on 2001 cars so i'm assuming there isn't much different between the two..

 

Thanks for the response. I happen to have access to a GM MAP sensor, and will go ahead and swap that in tomorrow, assuming the cleaning of the EGR tube doesn't work out.

 

When you pull the battery, most people recommend 20-30 minutes.

But you might want to also change the DPFE (Differential Pressure Feedback Egr) sensor and replace the EGR valve.

 

Good afternoon fellas. Thought I would report back and maybe help out some tech's in the future.

Yesterday I was able to pull off both the EGR valve and the throttle body. If you didnt already know the EGR will recirculate exhaust gases back into the intake manifold. On my dad's car (3.4L in question from the first post), after the EGR valve there is a winding passage which "U"s up into the intake. What had happened is through out the years, deposits had built up in that U section leading into the intake.

It was literally packed solid from the hole in the intake all the way to the curved part of the passage. It took me about 45 minutes to chisel through all of this and make sure that there was now flow through that passage. EGR flow insuffient wasn't detailed enough, EGR flow non-existent would have been the proper code to be set

I was playing around with the scan-tool last week while diagnosing this code, and was able to set EGR valve to be open 100%. Under normal conditions the engine should have stalled, instead it just ran alittle rough, almost as if there was a vacuum leak somewhere. After cleaning the EGR passage out completely, setting the EGR open to a certain percentage, well as expected, the engine now stalled out. Awesome, passage open, and EGR flow should be fine!

I cleared the code, and while it's only been a day, I don't expect to see p0401 anytime in the near future.


Thanks to all that replied to my original post...
Michael

 

Wow!!! Nonexistant!!! That's a little on the slow side for throwing a codein my book Glad everything worked out for you and you were able to fix the problem.