1996 Honda Accord P0401 Code: How to Fix EGR System Issues and Clean Intake Ports

Is your engine a V6 or a 4-cylinder? If it's a V6, you'll need to remove the upper intake manifold and clean it directly. For a 4-cylinder, there are two common designs: one involves removing the fuel injectors and accessing a long plate along the intake runner—this plate has a row of 10mm screws and can be removed for carbon cleaning. The other design requires drilling out carbon plugs in the intake runners and replacing them with new ones—a more complex process. I'm not certain about the exact model year split between these designs, but it's worth checking your specific engine configuration.

I have a 4-cylinder VTEC engine—thank you for the response! What is the best tool to remove carbon buildup? Do I need to make my own? A wire brush or pick would work, but what's recommended by professionals? Jason

No—the catalytic converter does not cause a P0401 code. Your VTEC engine should have the intake plate under the injectors. Look for a row of 10mm screws—once removed, you can scrape off carbon buildup. Also, check each intake runner for small holes; these must be cleaned as well. Once you start scraping, you'll see exactly what I'm describing. A pick or screwdriver works well for this task.

Thanks for the help! That was exactly the issue—three out of four intake ports were severely clogged. The plate under the injectors was also dirty, but once I opened it up, it became clear what was blocked. Cleaning with a small screwdriver and shop vac went smoothly. Jason