I have a new to me 07 MDX with 82k miles. Exactly at 1 mile over the 30day/1200 mile used car warranty the Check Engine Light illuminated along. The NAV screen showed an emissions code P0401. I really don’t notice any symptoms in running at all. Anyway a few drives (on/off) and it turns off for four days. It happened again with same code. Again few drives it went off. It seems to happen when driving easy. It gets great MPG in mixed driving on average (20MPG) which is far better than its rating.
Should I wait till it stays on steady before I address this?
That code indicates insufficient Exhaust Gas Recirculation (EGR) flow.
Even if the engine seems to be running properly, a poorly functioning/non-functioning EGR system increases the amount of pollutants coming out of your exhaust, and that is not a good thing. Additionally, it can cause very high temperatures inside the cylinders, and this can lead to “pinging” and engine damage.
I would advise you to try cleaning the EGR valve and its related plumbing.
If that doesn’t work, it may be necessary to replace the EGR valve.
I may try a peek if not too difficult. I have a factory service manual on order from ebay. My mechanical skills are limited but troubleshooting strong.
However that being said can this be diagnosed without the light illuminated?
You’ll want to take the cover plate off the upper intake manifold, and carefully remove the gasket under it. You’ll find carbon buildup along the EGR passages, possibly completely blocking 1 or more of the 6 holes.
I did this on my Odyssey. Carefull not to drop too much carbon residue into the intake manifold. You can take off the upper part of the manifold if you want to, but probably not necessary. Don’t do what I did and put that gasket back on upside down, make sure the holes line up.