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Old 04-24-2010, 07:44 PM   #1
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Default P0401 again

I'm getting a P0401 again. I took the EGR off today and cleaned it. Looked pretty good and wasn't really very dirty.

Not sure if I need to take off the TB and clean the ports up to the SC. I tried a test I read about, I took a 9 volt battery, connected it to the outside leads of the EGR while the engine was idling. I could hear the EGR click and the engine started to run very rough but didn't stop running. Makes me think that I can't be completely clogged if it is carbon.

This diagnostic was in regards to a 3.1 and the engine was supposed to stop running. Any thoughts on my next steps and if anyone knows should a 3.8 stop running on idle when the EGR is opened?
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Old 04-24-2010, 07:54 PM   #2
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Take a look here.
https://www.gmforum.com/showthread.p...82#post1390970

Running rough when you open it suggests to me a vacuum leak.
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Old 04-24-2010, 08:56 PM   #3
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See the below link. Running rough when open is normal or it should even stall out according to the below.

http://www.wellsmfgcorp.com/video_egr_hq.html
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Old 04-24-2010, 09:01 PM   #4
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OK, I see what your doing now. Opening the valve like that opens the system to the exhaust letting in unmetered air, ie, a vacuum leak. I misunderstood your first post a bit.
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Old 04-25-2010, 01:59 PM   #5
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I've been having this code a lot too. Even after my adventure the previous couple weeks.
So- I decided to pull the EGR like you did and was surprised at how clean everything was. So I doused and cleaned it all up, plunger moved freely- like I said, did not see the buildup I was expecting.
Reinstalled the valve and plugged it up- did some short driving runs and no codes coming up yet. I did notice it popping when I first started it up (popping meaning, I could hear the solenoid activating).

fwiw- since I got my scanner- I've helped out 4 friends with their car! and then fixed em all themselves!
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Old 04-25-2010, 03:20 PM   #6
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It don't take much to disrupt the valve movement. Sometimes you may need to clean it more then once to make sure.
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Old 04-25-2010, 04:40 PM   #7
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Spoke too soon- back again.
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Old 04-25-2010, 04:44 PM   #8
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A crack in the EGR tube can also cause this code. It'* also hard to find by simply spraying carb cleaner around it. Pulling to tube and looking for light leaking is the best way to find the leak. The cracks show up under the clamp most of the time.
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Old 04-26-2010, 08:50 AM   #9
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Hang in there a second.

Dan.. are you saying that a cracked EGR tube may cause this code? Wouldn't that be a too much flow or lean code instead of a insufficient?

The name of the code not being listed in the thread is a detriment to the thread.
P0401 EGR SYSTEM INSUFFICIENT FLOW

Here'* the GM FSM info on the code.
http://gearchatter.com/viewtopic9016...f22f51cf703f80

I've seen many guys spin their wheels checking the EGR etc because EGR is named in the code. The problem is usually not an EGR though. The system reads the flow at the MAP sensor. If the MAP doesn't see a change in flow as it'* expecting when actuating the EGR, it sets the code. Please check your map sensors and the vacuum lines going to it if you are supercharged.
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Old 05-01-2010, 01:08 PM   #10
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Thanks for the info. My bad, I did not realize that the code didn't automatically reset after I cleaned the EGR so I will disconnect the battery or borrow a scan tool to reset the code. If I still get the code I will start to review the steps you've listed such as looking at the map sensor. I don't think this is a cracked pipe as I should start running rough but I'll leave all options on the table for now. The engine is running great, no rough idle and I had replaced most of the vacuum lines when I did the lower intake gasket.
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