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Hey,

Let me start by saying that I tried to search multiple times, but it appears the website's search database is down at the moment. I keep getting error messages.

Anyhow, I've got an '04 Automatic Coupe that has been throwing a CEL the last couple days. The car runs fine and still gets good gas mileage. I went to autozone to have the codes checked, and it's throwing 401, which according to the sticky on this forum is:

P0401 Exhaust Gas Recirculation Flow Insufficient Detected

The employee said it could just be a vacuum hose coming off or something. I work on military aircraft so I'm confident I can do whatever maintenance / troubleshooting is required, I just haven't worked on cars much so I don't really know where to start. I have access to any tool I could possibly need including multimeters. Where should I start?

 
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First step, DX LX OR EX??

DO you have an aftermarket exhaust, turbo, or any engine mods?

 
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Sorry, should have specified earlier.

It's an '04 LX with a completely stock engine and exhaust system.

 
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2 real possibilities, vacuum leaK, which is not likely. or u have a clogged egr port somewhere. the egr valve, which is on the passneger side of the head connected to the water neck, has small ports that do tend to clog on our cars. this will not effect gas mileage or power, it is simply for emissions, so u would fail an emissions test, but u can try intake cleaner(seafoam) and see if it helps

 
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Thanks for the reply!

Gonna start troubleshooting. I'll let you all know what I come up with.