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Monte Carlo & Lumina Since the 1970s, the Monte Carlo has been an icon of American stock car racing. A 4-door version, the Lumina, was produced in the late 90's.
Platform: A-, G-, & W-body

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Old 07-05-2011, 02:00 PM
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Join Date: Jul 2011
Location: MD
Posts: 1
Default 99 Lumina with 3.1, P0401 trouble code

I can't seem to get ride of the P0401 EGR insufficient flow trouble code. I first replaced the EGR valve with an AutoZone "Duralast" valve. I checked the intake manifold passage and exhaust pipe passage, both were clear. The "service enginesoon" light went out for about 4-5 weeks. I thought I had fixed it. Soon there after the light came back with the same code (P0401). Some research I found indicated that a bad MAP sensor could cause this. It was cheap, so I replaced it. No help. Now thinking the AutoZone (Chinese made) valve may not meet GM standards, I purchased an OEM Delco EGR valve. This time I blew air intake cleaner into the manifold passage, removed the air snorkle and blew compressed air into the passage....all clear. I could see and hear the compressed air going into the manifold. Next I blew compressed air down the exhaust pipe and it was clear. Next I started the engine with the EGR removed. The vacuum side would nearly suck your finger into the manifold. The exhaust side would blow your finger off....ALL PASSAGES ARE CLEAR. I put the OEM valve in place and cleared the code. Everything was fine AGAIN for about 6-8 weeks. Now the code is back and I have no idea what to do. Please send any ideas you may have. I have heard that a bad PCM can do this. The car has 172,000 miles and runs great. No performance issues.
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Last edited by National1; 07-06-2011 at 06:18 AM. Reason: misspelling of a word
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Old 08-05-2011, 06:36 AM
CF Beginner
Join Date: Aug 2011
Posts: 3

I had that same exact problem with my 98 Lumina. I had no performance issues, and the passages all seemed to be clear. I still blew cleaner down them for good measure, but it wasn't until I removed the air intake assembly and visually saw the junction between the hot exhaust gas and the intake air that I found a most impressive partial obstruction that still hadn't come out in spite of my efforts. A little well targeted carb cleaner and a screwdriver fixed it after that.
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Old 08-05-2011, 06:36 AM

1999, 99, carlo, chevrolet, chevy, code, egr, gm, lumina, monte, obd, p0401, po401, trouble, w

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