P0401 Honda Accord, Cleaning EGR Passages

I know I’m jumping around but it will all become clear in the end, I hope. This is once again that same Accord that I worked on but this time I focus on cleaning the EGR passages. Over time these passages become clogged with what is called “hard carbon deposits”, many speculate as to the origins of this material but it is in my opinion the product of condensation and carbon buildup inside these passages that seems to contribute to this problem. The fix is pretty straight forward as you can see but the diagnosis can be tricky at times. Sometimes the check engine light will come on for an EGR flow code, but on earlier models EGR flow is not detected by the ECU and in those cases it might manifest as a failure of an emissions test for high NOx emissions. When this is the case the symptoms sometimes include, surging on the highway or a misfire under load. For the most part EGR’s are easy to check but there are some EGR systems that are very difficult to service and repair. All I can say is to consult with the service manual or a knowledgeable tech whenever you run into a system you’re not familiar with.

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