2015 Infiniti QX80 just ticked over 100k miles. 1 month ago, P0430 pops on (catalyst below threshhold)- I reset the code just to see if it would come back. 2 weeks later, it's back. I then change all 8 plugs for the 5.6 V8 and ran a bottle of BG44k through it. Today, 2 weeks later, bank 1 P0420 kicks on.

My voltage readings for both bank 1 and bank 2 are:
B1 S1 (wideband) 2.25V
B1 S2 .280V

B2 S1 (wideband) 2.255V
B2 S2 .260

From what little I know about wideband 02s, the 2.25 V is telling me it's running rich at idle...Which I suppose would make sense as to my cats trying to die at 100k. Any wizards on the AB with insight into 02s and Nissan engines? Not sure how I get both banks throwing a code within 1000 miles of each other. This is a Sewell Dealership QX80 we've had for 5.5 months and 6k miles of driving. To replace each manifold/cat, that's going to be a Sheet ton of money which I won't spend.

O2 sensor, vac leak, or throttle body could all cause issues.

Assuming no other issues are prevailing, this is a sign of a catalytic converter losing efficiency.

Basically the ECM is measuring the difference between 2 o2 sensors 1 up stream and one downstream of cat.

There should be a large difference in O2 readings. If not, check engine light.

Those readings on the O2 look a bit high for being the downstream 02s. I would expect something on the order of 0.05-0.15.

What are your short and long term fuel trims?

Spark plug spacer.

My wife has a '13 QX56, so same drive train, and hers did this a few years ago. I replaced air filter, plugs, and cleaned MAF sensor but that didn't fix it, so now I just get it inspected when the light's not on and live with it.

Please post here if you figure it out.

I'm taking it in next Monday for a full evaluation. I don't plan on fixing it yet if they tell me it's the cats. I'll report back with the news/updates.

@1ags - I don't know the fuel trim just yet. I can scan it this weekend and see what I find.

Sorry, it is called a spark plug non-fouler. That is what you need.

Did the evaluation turn up anything?

My Ford does the same thing. Dirty exhaust from oil intake eventually can damage the converters, requiring replacement. Either live with it, replace the converters, or truck the o2 sensors by various means to stop sending codes.

Rarely, it could be the sensors, but that's unusual. I know different engine, but it's typical of many engines these days.

We had this problem in a Toyota FJ Cruiser. Replaced a cat & that fixed it.

Car is at Sewell as of today. Will report back with any news.

That's what I'm banking on…being an issue to live with or to sell items . No way in heck I'm paying 6 grand to replace both sides.

Replaced cats at 95k and 100k under CPO on my 2013 QX56 and now needing both again at 200k….

Happy to bypass the second O2 sensor to make the CEL go away if anyone can explain how. Not spending $$$ on Cats for this 200k vehicle.

Sensor bypasses $30 online. New cat $1500 installed. Hmmm.

Received the call I was expecting today. Both cats need to be replaced. Sewell did however offer to drastically reduce the cost to something more palatable...still substantial, but less than half of what I was expecting.

I could place the space on the 02..however, my concern is failing inspection...(although I cannot recall inspection techs looking under the vehicle)...maybe they do though. But that is my concern. I have a 30 day standing offer to replace them.

I still wish I knew why these Infiniti cats take a dump at 100k almost on cue. Is the 5.6 V8 hopped up and running rich from the factory?

Read the words I typed in an earlier post.

Milwaukees Best Light said:

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Sorry, it is called a spark plug non-fouler. That is what you need.

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So you'd install this where the not-spark-plug screws into it? Do you need to put these on both up & down not-spark-plugs?

I found these are necessary for one side of the QX56 due to transmission pan.

https://www.ebay.com/itm/90-Degree-Oxygen-Sensor-Spacer-M18x1-5-O2-Spacer-PACK-OF-2/122455092755?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649&mkcid=1&mkrid=711-53200-19255-0&siteid=0&customid=link&campid=5338699689&toolid=20001&mkevt=1

Get under truck
Unscrew last O2 sensor ( furthest rear)
Screw in spacer
Screw in O2 sensor into back side of spacer
Drive 40ish miles
Light goes out
Sell the car at some point (supposed to be some kind of vacuum issue that will eventually kill the engine), not sure how quickly you need to get out. I think you will be good for quite a while.
Profit

I asked to have my cats/manifolds back and Sewell is telling me there is a $140/each core charge on them...??? Aren't these my damn cats that I can take for free? I assume I can get $200/each for them.