Hey guys. I have the dreaded po420 code on my max. It has been coming on and off for nearly 9 months now. It tends to stay on for about a month then turn off for a week then come back on. I assume that this is due to my y-pipe and that all my oxygen sensors are actually working correctly. The car has plenty of power so that rules out my cat and there doesn't seem to be an exhaust leak. My gas mileage is down, I have not calculated it but I can see my fuel level dropping faster than normal. What do you think my chances are of fixing this problem for good with an installing an o2 simulator in place of the rear o2 sensor? Any other suggestions on diagnosing this problem before buying the o2 simulator?

 

I'd at least take a look at the readings of all the o2 sensors with a scanner, and/or depending on mileage just replace them. I've seen o2 sensors, both primary and secondary, cause the cat efficiency code more times than the actual cat. Also check for other obvious problems like maintenance up to par, with no exhaust or intake leaks. Nissan cat's are fairly "bulletproof" IMHO, the only times I remember having seen them go bad it was due to an excessively rich condition or from coolant contamination after putting a motor in from a bad headgasket.

 

I have a brand new o2 simulator if you want one. I purchased it from o2simulator.com. He wants to charge me 20% restocking plus shipping to return it. I'd rather sell it to someone on here. $20 Shipped.

 

not to jack but i have a high flow cat and warpspeed y. i get the 420 code and a code for o2 as well cant remember whichone, but it's one of the front ones. when the y and cat were installed the o2 behind the cat spriped out and was replaced with a new one. i think the front 2 o2s are original. should i try and replace both fronts because the lazy readings from them compaired to the new rear is what is throwing the codes, or would it make more sense just to sim them?

 

For me it was my O2 sensors. This code liked to periodically come up and it would come back after a few hundred miles of resetting it. I fixed them by simulating them when I did a fed-spec conversion and a y pipe.

 

Fixed

 

i had this issue because of a SMALL leak near where the pipe meets the headers.

once i removed and remounted everything, the code stopped showing up.