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.

 

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.