98 Malibu EGR low flow (code P0401) - Chevrolet Forum - Chevy Enthusiasts Forums

98 Malibu EGR low flow (code P0401)


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February 5th, 2008, 3:40 PM   #1  
98 Malibu EGR low flow (code P0401)

Hello, I am new to the forum and would appreciate any help that can be given. I have a 1998 Malibu that has a continous CEL (code P0401) low EGR gas flow. I pulled the EGR valve and cleaned it thouroughly (wasn't really that bad), also blew out the channels with compressed air, and de-carbonized the engine with Sea-Foam while I was at it. After resetting the pcm the code stayed off for about a week, then returned. A new EGR valve is 180$ where I am at and I feel that is a bit much to change out while "shot-gun" trouble shooting, especially since I have heard of other sensors to blame, or a clogged intake (50$ for new intake manifold). What I would like to know is if there is a way to check the EGR valve or other related sensors, if so please explain. Don't want to pull the intake manifold off due to very little carbon build up at the EGR. Am more than willing to follow advice given, within reason and cost effectiveness of course, and report back my findings to hopefully help others. Thank you in advance for any help or suggestions.

 
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February 7th, 2008, 10:04 AM   #2  
RE: 98 Malibu EGR low flow (code P0401)

you can test the egr very easily pull off the vacuum line going to it hook up a vacuum pump to it ( very cheap like 15$ at checkers) when you apply vacuum at idle you should hear the motor running a little rougher since you are adding burnt gasses it will lean out the mix and make it run rough. if it doesnt change anything then the diaphram in your egr is bad. if it does change then you could have a controll issue with the egr controll unit usually has two to three vacuum lines on it and could go bad also.

 
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February 7th, 2008, 9:19 PM   #3  
RE: 98 Malibu EGR low flow (code P0401)

The Valve on this car is electronic, so, unfortunately a vacuum pump will not work for testing.
If you have a scan tool, you can command the pcm to open the valve to see if the valve itself is working.There are really only4 things to go wrong with these things, PCM, wiring,the valve itself, or plugged passages. I have never seen the pcm cause this problem, or the wiring for that matter. If you say you have pulled the EGR and checked the intake passages, then I would be pretty confidetn in saying the the egr valve itself is bad.

 
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February 8th, 2008, 8:28 PM   #4  
RE: 98 Malibu EGR low flow (code P0401)

I was told that there were also several other sensors that could send this same error. I would like to try jumpering the EGR to listen for the click, or even pull it off and watch it move, but I doubt that it runs on 12 volts. Does anyone know what voltage is sent to the EGR to open it? Unfortunately I do not have a scan tool to do it with, didn't know that the normal scantool from walmart (about 60$) could tell it to do that. Can it? Thank you all by they way for the help so far.

 
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February 9th, 2008, 11:46 AM   #5  
RE: 98 Malibu EGR low flow (code P0401)

I have never seen another sensor throw an EGR code. That code is very specific to the EGR itself. The code is set when you are driving, the ecm commands the egr to open, and it doesn't see a slight drop in RPM andthe O2 sensors don't go slighty lean. I guess it could be the fault of the O2 sensors, but you would more than likely be setting off codes for it as well you would see a change in fuel mileage

 
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August 5th, 2011, 10:20 AM   #6  
Partial Blockage

I had a similar problem with a 3.1 engine on a Lumina. There was a partial blockage at the junction with the exhaust gas and the intake air just behind the air intake assembly. The blockage didn't seem to effect the performance, and it wouldn't come out from any cleaning attempt short of taking that intake assembly off. In fact I couldn't even tell if it was there or not until I took it apart. However, it did cause the car to throw the P401 code for "insufficient EGR flow".

Once I finally resigned myself to removing that throttle assembly, the fix was very easy. Just make sure you have a full can of carb cleaner on hand.

 
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August 5th, 2011, 11:16 AM   #7  
With a TechII (official GM scanner tool) the EGR can be commanded to do certain things and there is a whole diagnostic section in the manual for determining whether the EGR valve is bad using said TechII. I don't think just any ole scanner can command the EGR valve to do anything.

Partsgeek.com shows the 4 banger egr valve @ $145.98 and the V6 @ $137.98. I usually find shipping from there to be around 8 to 11 dollars. Don't forget the gasket.


Last edited by Tyrod; August 5th, 2011 at 11:22 AM.
 
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