A Honda Odyssey came into the shop with a check engine light. I hooked up the scan tool and found the codes P0400 EGR System Leak and P0430 Catalyst System Efficiency Below Threshold. The first step to diagnosing an EGR leak is to do a visual check for leaks. When I got the van up in the air, I found the problem very quickly.
The EGR pipe goes from the front cylinder head and connects to the front exhaust pipe just below the catalytic converter. I don’t know this would’ve happened, but there were no nuts on the pipe connection. This meant that the pipe separated from the exhaust, causing a definite leak. It’s likely that this leak also confused the computer and caused the P0430 code as well. After installing new nuts, I took it for a test drive and it passed the test for both codes.
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