EGR low flow. Replaced EGR, still getting code - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1992-1999 Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's and Buick Lesabres Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 03-13-2005, 01:03 AM   #1
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Default EGR low flow. Replaced EGR, still getting code

As if the power steering headache and vibrating front end weren't enough, I also have an EGR problem with my 1997 L36. I got a P0401 EGR flow insufficient code, while cruising around 50-60 mph, a few weeks ago. I replaced the EGR valve ($150 for a Wells) and cleared the code. The code came back 100 miles later. I cleared it, very angrily. The SES light stayed out for 500 miles this time, and then came back on. P0401 again. What the hell! I don't understand how I can intermittently have low EGR flow even with a brand new valve. I did upper and lower intake gaskets on this car a couple thousand miles ago and there was nothing obstructing the EGR passage. I also was very careful not to damage the bendy straw EGR tubes (I think)
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Old 03-13-2005, 07:50 AM   #2
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If the valve is working properly and the passages are clean, that would point to the wiring or the PCM.
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Old 03-13-2005, 12:49 PM   #3
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Welcome to the false code club! I had the same problem....spent 170 on a new gm valve....the lite came on and off for about a year....turns out there was corrosion inside the pcm that was shorting out the computer ....causing egr problems....I removed the computer from the aluminum case and saw aluminum flakes peeling off the inside of the case....it sounds like you may have a similar problem....or else your puter is malfunctioning on its own....
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Old 03-13-2005, 03:37 PM   #4
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Hay 1997_LeSabre do you have a service manual that explains how the PCM tests for P0401? If I had a scanner I would post it here for you.

The PCM tests the EGR system during deceleration by momentarily commanding the EGR valve to open while monitoring the Manifold Absolute Pressure (MAP) sensor. When the EGR valve is opened, the PCM should see a increase in MAP. (A drop in manifold vacuum.) If the expected increase in MAP is not seen, the PCM notes the amount of error that was detected and adjusts an internal fail counter towards a fail threshold level. When the fail counter exceeds the fail threshold level, the PCM will set DCT P0401. Bla bla bla.

Conditions for Setting P0401
The PCM has to see all sensors working OK and have no other DTC codes.

TP angle is less than 2%

Coolant temp above 180*

RPM between 800 and 1400

IAC position is steady

Vehicle speed is above 23 MPH

MAP changes monitored during test indicate low EGR flow

This is just the first paragraph hope someone can copy and post the whole thing.
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Old 03-13-2005, 04:08 PM   #5
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Ron, I don't
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Old 04-20-2005, 02:48 AM   #6
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Default change the pcv valve... believe it or not

i finally solved the problem with the P0401 CODE on my 97 bonneville 3800 vin K

believe it or not, it was caused by the repair shop leaving the PCV valve out when they changed the upper plenum...

it sits directly below the MAP sensor... they swapped the plenum and left the PCV valve in the old part... it caused the code to set...

i found out, that code is more about the MAP SENSOR'* ability to sense pressure change in the intake manifold when the egr valve is commanded on by the computer, than whether egr gasses are flowing or not...

since the pcv valve was missing, the MAP SENSOR was sensing no change in the intake manifold pressure, which told it the egr wasn't flowing... but it was really the fact that the PCV VALVE wasnt allowing the manifold pressure to build to a point that it could drop when the egr opened.... this in turn sent a false signal to the MAP SENSOR...

all over a missing PCV VALVE...
now a faulty one, (sticking open) could cause the same problem....

hope this helps you...

check or replace the PCV VALVE cheap insurance for less than $5 bucks..
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Old 04-20-2005, 02:59 AM   #7
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And make sure the O-rings are installed as well.
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Old 04-20-2005, 09:17 AM   #8
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I had an EGR code just pop up. Everytime I started the car it was gone... and would reappear when it wanted. Aggrevating to say the least since like you I was in the middle of other problems too.

By replacing the EGR gasket (when I attempted to clean the EGR) and reseating the connector to the EGR about 5 times (thanks to whoever posted that I should try that) something worked itself out. Now I'm giving my car the royal treatment. Anytime I take apart a connector I make sure it'* clean and good, then add a little dielectric grease to it. The dielectric stops corrosion and promotes good conductivity. I've noiticed with the age of some of the cars we have corrosion over the years...
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Old 04-20-2005, 10:06 AM   #9
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Default dielectric

I allways use dielectric a on my electrical.
Just installed the Delco ign. on my 90, cleaned, tightened, and applied dielectric to the ICM, and coil wire connections.
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