Odd issue with a P0420 CAT efficiency code over the last several months. Code comes/goes every few weeks, to months. Cats were replaced around 235K when they were bad. Engine rebuilt at 253K after the great power valve down in the engine problem...thanks Nissan. At the moment I'm at 267K and this has been happening over the last several months. I know when it happens, and how to recreate the code...but not sure what the problem really is. This pathy is run just about every day of the week, and rarely sits. As long as it is run, no errors. If I let it sit for two or three days, I get the code. I can park it with no codes or pending codes. Let it sit for two or more days, and then start it, and immediately within just a few seconds as fast as the code reader can monitor I have the P0420 pending. Reset it, and no P0420 until I let it set for a while again and restart it. And when it engine starts it's not bad, but not smooth either. In about 5-10 seconds after starting, it's running perfectly. During those first 5-10 seconds after sitting for a few days it's just a bit noticeable that it's not perfectly smooth. Almost like the days when the old distributer cap would get a bit of moisture in it...of course, no distributer cap in this. I don't think it's moisture (rain) as I can let it sit out in the heavy rains and storms, and as long as I run it every day, it's fine. I can let it sit two plus days in perfect sunny weather, and I still get that not perfectly smooth start with the P0420....and only the P0429.
When it was rebuilt 14K ago, all new filters (gas too), new NGK platinum plugs, anything "maintenance" was done in addition to the rebuild. It still does have the original factory O2 sensors...wondering if that could have something to do with it, and if so, which ones would most likely be the culprit. I'm not really wanting to start replacing parts to "see" what fixes it at this point. I'd like to get to the bottom of the problem. I still travel a lot in this, and don't want to get stranded somewhere because something "fails" and I'm far from home. Thoughts? - And no, I'm won't buy a new one...as long as Nissan continues with the CVT crap!