2006 G35 Sedan.

SES light came on. Took it to local auto parts store, ran a free diagnostic. Gave me code P0420 which reads --- Catalyst System Efficiency Below Threshold (Bank 1)

No other codes are with it. Just that. Randomly happened as I was driving home from work. So I searched around, and found out that most of the people with this code, have other ones along side. One being the P0430 code.

Thats the same thing as above, just bank 2.

So whats the difference between Bank 1 and Bank 2? Since my issue is only bank 1. Passenger side?? Does that help me find out what is causing this code of P0420 that I have??

Only symptoms my car is experiencing since this happened is bad gas mileage. NO problems idling, driving, going uphill, exhaust smoking or loss of performance when at WOT.

Thanks y'all, I just dont want to have to replace parts that aren't even the issue.

 

If it is oxygen sensor, which one could be the most likely culprit? Before the CAT or after?



After work I'm going to search for exhaust leaks and check wiring to sensors. Sorry I'm just at a loss for this issue.

 

Bank 1 is passenger side so you are correct there. The only difference between bank 1 and 2 is the left or right side of the engine. Being a V6 it has 2 banks as opposed to a Inline 4cyl engine which only has one. If it is a catalyst issue and it is a faulty o2 sensor it would most likely be the post cat. Your post cat o2 sensors are there for referencing to see if the cat is doing its job. (emissions) I know on my '06 coupe the primary o2 sensors are wide-bands and the secondaries are regular narrow-bands.

[ After my headers and HFC's install I was getting both P2A00 & P2A03 codes, those are bank 1 & 2 primary (before cat and in manifold/header) o2 sensors. Turns out the added exhaust flow wasn't making them happy. With a little tweaking via UpRev, it cleared it right up. Some tuners even disable the secondaries and make it so your ECU doesn't even look for them. Seeing how I still have cats {even though they are high flows} I decided to keep them enabled. ]

Swing it by to auto-zone, pep-boys, oriellys, etc.. and have them clear the code and see if it comes back before you go crazy. They do it for free as you know. You can also check the voltage from the o2 sensor and see if its working correctly. Narrow band o2 sensors roughly increase and decrease voltage consistently between 0-1v (.2-.8v) to be more specific. Worst case your ECU is now running open loop and gas mileage will suffer a little until you pinpoint the culprit and get it fixed.

ECU Modes:

OPEN LOOP - this is the mode your ECU is in until the coolant temperature and a couple other sensors get to operating values. This is also true when you are at WOT or when throwing codes/ CEL's

CLOSED LOOP - the ecu uses information primarily from the Oxygen Sensor and adjusts fuel delivery and timing to achieve minimum emmisions, better gas mileage and power

Check out this link;

http://www.obd-codes.com/p0420

Here are some pics for reference. Hope this helps.

 

Thx man, preciate that help.



My only question is, why do you suspect it would be the sensor post cat than the first one? I def will check out that voltage to try and narrow down. Gut feeling telling me its a sensor, so I want to try the cheaper route first before messing with the cat. Thanks for the help!

 

No worries! I was just saying if it was indeed an o2 sensor causing the problem, I would think it most likely be the post cat. I ran into a similar issue with my Frontier and it ended up being the post cat sensor, but I did have a code for the sensor as well... (slow response)

Hopefully it ends up being the post cat as it is very accessible and easy to change out compared to the primaries and a lot cheaper!

It is strange however you are not getting an actual o2 sensor code, or any other code for that matter as you stated... In the link I attached it mentions probable causes, but you do not have a o2 or misfire code.

I would, if it was me I would throw in fresh premium fuel, maybe even some lucas, make sure the gas caps tight, drive it for a bit, have them clear the code and see if it comes back. If it does maybe it will have additional codes to aid in troubleshooting.

Emission related SES lights/codes can be a goose chase and you could end up spending way more than you should via shotgunning parts at it. It may very well could be a bad cat. Hopefully its not. That's where troubleshooting and voltage check comparisons come into play. Here some more info I came across;

" Air leaks at the exhaust manifold or in the exhaust pipes.Catalytic converter is damaged, contaminated or it has failed.ECT/CHT sensor has lost its calibration (the signal is incorrect) Engine cylinders misfiring, or the ignition timing is over Engine oil is contaminated. Front HO2S or rear HO2S is contaminated with fuel or moisture.Front HO2S and/or the rear HO2S is loose in the mounting hole.Front HO2S much older than the rear HO2S (HO2S-11 is lazy).Fuel system pressure is too high (check the pressure regulator).Rear HO2S wires improperly connected or the HO2S has failed.Here is the causes for the code.It's a process of elimination,till problem goes away. Could be Oxygen sensor,but maybe not."

Try the easy first and let me/us know what you find out.

 

Just a heads up, I am actually deployed right now, but I do have a set of oem cats with 46k on them if that is the problem and you are in need of them. I would only charge you whatever it would cost to ship them if it came to that... I'm sure they would be the same for the sedan, but research it to verify. They are sitting in a box in my garage collecting dust and I'm all for helping people out!

Also, If it does end up just being an o2 sensor I would recommend sticking with oem if you have the funds. Call your local Nissan dealership as parts are typically cheaper than Infiniti. If money is really tight, you can pick them up used off good old ebay for next to nothing. Make sure to use high temp anti-seize on the threads only. New ones should all come with some pre-applied. As far as the oem metal exhaust gaskets are concerned, they usually can be re-used. I usually use high temp copper gasket spray for added security.

 

Thanks man, I'm at work now but I'll check it out in a few hours and keep posted.