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P0401 Buick 3800

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14 Jan 2020 13:08 #36603 by kdub12003
P0401 Buick 3800 was created by kdub12003
Hello everybody! New here and need some help. I am working on a 2001 Buick Park Avenue with the N/A 3.8 Liter. Car was sitting for some time and had multiple issues but one that I cant seem to sort out and that is the P0401 code. So I will list the work that has been done and the tests that have been made so far. We performed a complete tune up with spark plugs, spark plug wires, all filters and fluids changed and a PCV valve with both o-rings. The car had a P0401 when we got it and digging into that there were some vacuum leak concerns and a coolant leak that prompted us to remove and reseal the upper and lower intake manifold and throttle body gaskets. The car also has a new EGR valve and MAP sensor. While the intake was off we cleaned all the EGR passages and believe them to not be obstructed in any way. I verified that the tubes were not leaking with a smoke test and also did this on the intake plenum to check for vacuum leaks and the EVAP system, all tests passed. The car runs perfectly and fuel trim data shows that a 14.7 AFR is held with almost no fuel added or taken away, the EGR commanded values and actual values as well as MAP rise during a drive cycle seem to be spot on and the EVAP purge and vent circuit seem to be working properly. This code will be set in about a mile during a test drive after clearing it every time with no other fault codes or indication that the engine is running poorly. I also inspected the entire exhaust system for leaks and found none. I performed all the EGR tests, however even when holding the valve open at 100% with a jumper wire the engine never would stall although it will run extremely rough. I can do this with my scanner as well but cant get it to command over about 89% while asking for 100%. Pintle position reads correctly and it is a new Delphi valve and has a new gasket as well. I believe the only part if the system I have not verified a problem or not is the catalytic converter, which on this car there is only one. I have read every forum, every TSB, and watched every video I could find and this one has me stumped! If anyone has experience with this any help or push in the right direction would be greatly appreciated!
Thanks, Keith

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14 Jan 2020 14:45 #36606 by scannerjohn
Replied by scannerjohn on topic P0401 Buick 3800
engine should stall immediately when EGR is commanded open. passage way may still be clogged or EGR is not working properly. you're not getting 100% open command.


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14 Jan 2020 15:49 #36607 by kdub12003
Replied by kdub12003 on topic P0401 Buick 3800
Thank you, so in every case when you command 100% EGR it should stall the engine?

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14 Jan 2020 18:30 #36613 by Cheryl
Replied by Cheryl on topic P0401 Buick 3800
Think there’s a bulletin in these for a reprogramming of the pcm

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27 Nov 2020 09:51 - 27 Nov 2020 09:53 #44709 by GMP440
Replied by GMP440 on topic P0401 Buick 3800
A better way to check the EGR passages on the 3800 engine is to take off the EGR valve. Get two long rubber hoses that will fit snugly into the EGR ports. Have the hoses long enough so that you can hold them as you are sitting in the driver seat. What you will be doing is feeling for suction in one hose and air pressure coming out of the other hose which tells you the EGR passages are clear. Take one hose and cover the opening with your thumb. Start the car. If you feel suction , that port is clear. Shut the car off. Now, get the other hose. Cover the hole of the other hose with your thumb. Start the car, with the engine running , feel for air pressure coming out of the hose. If you felt air pressure from one hose and suction from the other hose, your EGR passages are clear.
Last edit: 27 Nov 2020 09:53 by GMP440.

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27 Nov 2020 10:31 #44711 by kdub12003
Replied by kdub12003 on topic P0401 Buick 3800
Update!! The new delphi EGR valve turned out to be causing the problem despite already being replaced. We replaced with the highest quality AC Delco unit available and the problem was solved. Cheap parts are cheap parts even name brand ones.
The following user(s) said Thank You: Tyler

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27 Nov 2020 13:28 #44713 by Tyler
Replied by Tyler on topic P0401 Buick 3800
Thank you for the update! :cheer: Very much appreciated.

FWIW, I've been down the same road with aftermarket EGR valves on GM's:

members.iatn.net/techmail/view/index.aspx?m=29947&t=gm_drive

tl;dr - Equinox got three aftermarket valves before a Delco fixed it. :silly:

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