So I started getting this code a few months back and it has been going on and off, I thought it might have been the fuel I was using or the fact that I misread the gauge one day and ran out of fuel. But it has stayed on the last couple of weeks. I'm due for my emissions testing which I know it will fail because of this issue.

I just want to know which side of the engine is bank 2 and weather its worth trying to replace the o2 sensor before replacing the CAT?

If I replace the cat I am gonna do both sides and replace with highflow's as I still need to put my Gibson Exhaust on still

I have 137000 miles on the Pathy, I never got an answer on who can read those voltages to check the O2 sensors

I have the P0420/P0430 code going as well on my 05. Truck seems to be running fine, and I can check the O2 sensor voltages with my Superchips tuner. My observation seems to point towards bad post-cat O2 sensors, as the voltage seems to be way off and quite variable, even 0 sometimes.

What I'd really like to do is hollow out the primary cats, and replace the secondary with the Doug Thorley pipes that SMJ used in his mod project. Probably some O2 sensor spacers for the rear sensors so I don't have the perpetual CEL. Probably get a few HP out of it, though it could also have a detrimental effect on back pressure, which can cause other problems.

Also note I live in an area that does not do smog checks, if you live in a carb state or anywhere they do smog checks, this would not work for you. Its also highly illegal, so I haven't done it either. Just thinking about it.

Yeah I live in a county where emissions is required unfortunatly. so that idea is out of the question. I was thinking about doing the same as SMJ but I don't have the money right now, but I'd rather replace the O2 sensor than the Cat at this point.

The only high-flow cats I could find for the R51 were universal fit units; I couldn't find any "direct-fit," high-flow cats to replace the upstream catalytic converters. The high-flows I've seen would be used if you installed long-tube headers and placed the high flow cats where the secondary converters are at the mid-pipes. If one wanted to install the oxygen sensors fore and aft of this converter, one would have to lengthen the wires of the O2 sensor sub-harness to reach that far back and install sensor bungs on the pipe. To be fair, factory converters usually don't create a lot of restriction in the exhaust system so long as they are not clogged or contaminated. I'm also not sure if gutting the front converters, eliminating the rear converters and installing rear sensor spacers will not result in a CEL trigger for P0420/P0430. Also, if you plan to use long-tube headers (and I imagine the same would hold true for gutting the factory upstream converters), you will need to have your ECM re-flashed (re-flashing can also prevent the catalyst efficiency code triggering, which would mean you don't need to install rear sensor spacers. If I remember correctly from my header research, removing the upstream converter causes the engine to run lean due to the affect on the upstream O2 sensors. If you are going to do all that, you are probably going to want a new ECM map, anyway, to get the full benefits of your upgrades. I'll probably be doing that once I get finished. UPREV seems to be the best route to go as they specialize in Nissan ECM tuning and reprogramming.

SMJ, are the cats California legal? And would your setup pass emissions testing?

According to this link Magnaflow have Highflow OEM Replacements, but these are Pre OBDII I'm guessing these are the pre Cats then I would have to get universal post cats?

SMJ is bank 2 the driver or passenger side?

All R51 Pathfinders, in fact, all US vehicles from 1996, are OBD II compliant.

My vehicle would pass inspection where I am in Virginia, but they don't do emissions testing here. I installed shorty headers with stock, upstream catalytic converters. I deleted the post cats with the Doug Thorley mid-pipes, but the post cats are after the rear oxygen sensor, therefore are not monitored.

Bank 2 is the left, or driver's side, of the vehicle.

So After running cataclean and a tank of premium the code seems to have gone away. So I'm gonna go take it in for emissions today LOL

Well that was short lived, enough to get me through emissions though which is what I needed for another year. Looks like I am gonna have to replace something