Got both codes. “Catalyst system efficiency below threshold” for both bank 1 and 2. No other codes.

What steps should I take to diagnose?

I believe the fact that both codes showed up without any other codes should eliminate some possible causes while increasing the chances of others. I’m hoping of course to avoid replacing the catalytic converter. Much thanks! And happy new year!!

When those codes are by themselves, the cause is always weak cats. You may get some extra miles out of them by installing spacers on the rear O2's, but be very circumspect about that. You're basically disabling the early warning system, and a cat that melts can be sucked into the exhaust valves with instantly-catastrophic results. VQ40's are less prone to that than some other Nissan designs, but that doesn't mean it can't happen. They're still Miller-cycle designs, and anything which Miller-cycles can inhale a cat under the right circumstances. So if you can afford new cats, that's the right answer.

VStar650CL wrote: ↑

Mon Jan 02, 2023 10:41 am

When those codes are by themselves, the cause is always weak cats… So if you can afford new cats, that's the right answer.

Hmm. What is a reasonable cost to get new cats installed? How might I save some $$$? Is it DIY-able?

Pathyj1 wrote: ↑

Tue Jan 03, 2023 7:18 am

Hmm. What is a reasonable cost to get new cats installed? How might I save some $$$? Is it DIY-able?

DIY-able if you have good tools and good skills. Probably 1.5 to 2 hours per side in a shop, the 2WD's aren't terrible but 4WD's are a bit of a pain. Give yourself a day jacked up in a driveway. You can save a lot by going aftermarket with the cats, but don't go bargain basement, I've seen China-cheap ones literally disintegrate in under 10K miles. My go-to is usually AP/Eastern Catalytic, decent price, good quality, and (very importantly) they usually fit right without any screwing around.

VStar650CL wrote: ↑

Tue Jan 03, 2023 10:41 am

DIY-able if you have good tools and good skills… My go-to is usually AP/Eastern Catalytic, decent price, good quality, and (very importantly) they usually fit right without any screwing around.

Thank you @VStar650CL.

I apologize for being high maintenance. Although I’ve done a wide variety of repairs on my multiple cars that are 20+ years old, this is actually my first time running into a catalytic converter issue.

I’m not sure what I have to buy. I’m in California so I know there are specific models for us. But there are some that are for the front vs. the rear, while some have additional tubes attached, and there seem to be gaskets and clamps involved.

Might someone be willing to provide a little more detail about what I need for my California 2001 4wd Pathfinder? And where would be the best websites to buy them?

Pathyj1 wrote: ↑

Tue Jan 03, 2023 2:11 pm

VStar650CL wrote: ↑

Tue Jan 03, 2023 10:41 am

DIY-able if you have good tools and good skills… My go-to is usually AP/Eastern Catalytic, decent price, good quality, and (very importantly) they usually fit right without any screwing around.

Thank you @VStar650CL.

I apologize for being high maintenance. Although I’ve done a wide variety of repairs on my multiple cars that are 20+ years old, this is actually my first time running into a catalytic converter issue.

I’m not sure what I have to buy. I’m in California so I know there are specific models for us. But there are some that are for the front vs. the rear, while some have additional tubes attached, and there seem to be gaskets and clamps involved.

Might someone be willing to provide a little more detail about what I need for my California 2001 4wd Pathfinder? And where would be the best websites to buy them?

I will always defer to Vstar's judgement in these things, but i understand it is generally only the front cats that need replacing and that trip the code.
the website i use is rockauto.com

I purchased the Walkers for my 2011 Xterra, but there are 2 levels on rockauto and i picked the higher one ( "daily driver")
I also looked for the brands Vstar mentioned since he and SMJ recommended them but i could not get them in stock at the time and the walkers (as long as its not the entry level walkers) were deemed decent enough.
rockauto.com will also sell any addtionla accessories needed to install the cat for a reasonable fee.
I orderd "flanges" for the cats but do not know if that is needed in your case.

Here is a search result, If you have emissions testing in your jurisdiction I would look for "CARB compliant" options , front cats.
Also if its a cali vehicle I understand the ecu may expect to see cali cats and throw a code if not.
however i am not 100% on that perhaps Vstar or SMJ could shed some light on that.

https://www.rockauto.com/en/catalog/nis ... erter,5808

Thank you @palmerwmd

When the rain stops I’ll get under the car to take a closer look at my exhaust system and figure out what I should be looking for.

This car has only 160k miles and is otherwise in good condition so I don’t think it’s yet time to give up on it!

It's just the front cats, and on an '01 they're separate from the manifold, not conjoined like, say, a VK56. For Cali you need CARB-compliant cats, which have a special number stamped on the casing and are usually half again the price of Fed cats. The ones I'm seeing in RockAuto are showing $350~400.

VStar650CL wrote: ↑

Mon Jan 02, 2023 10:41 am

When those codes are by themselves, the cause is always weak cats… So if you can afford new cats, that's the right answer.

Thanks for the purchasing tips. Before I pull the trigger on new cats, I could use a little more guidance.

Do these two codes typically show up together? I would think the two front cats are independent of each other so it’s unlikely the two codes would appear exactly at the same time.

I’ve seen other forums suggesting pulling the cats and as long as they are not broken up, cleaning them out first. Or replacing the O2 sensors first since they typically go out sooner, are easier to replace, and cheaper. Thoughts on these options?

Thanks for the input. I just want to get a bit more educated before laying down some hard earned cash.

You can try Cataclean, the stuff works pretty well for extending the life of dying cats which aren't quite dead yet. The only thing besides the cats themselves which (rarely) causes P0420/P0430 to occur in isolation is exhaust leaks somewhere right near the rear sensors. I can't recall how far back the Y occurs in an R50 exhaust, but if it's close to the sensors then a leak there could affect both. I did a little research and it turns out it's also possible you have faulty firmware in your ECM. There's a bulletin for it, NTB02-87a. Might pay to have the dealer or a shop with a high-end scanner upload your ECM part number to see if it applies:
https://www.tsbsearch.com/Nissan/NTB02-087A

More info. I read online that the temperature right after the cat should be significantly higher than right before the cat. If not, the cat definitely needs to be replaced.

After car was fully warmed up, my cheapo infrared temperature gauge tells me the temp before the front cat is 150 degrees F and 250 after. For both left and right sides. I believe the difference is supposed to be hundreds of degrees higher.

Does this confirm I need to replace both front cats?

Those temps don't sound like the cats were fully lit, they need to be for a fair test. Dunno if that's F or C either, if it's C then it isn't terrible. Even if it's F I'd try some Cataclean because they're still working some, just not well.

EDIT: Oops, missed the F. My bad. I'd still try some Cataclean and see if it kills the codes.

@ VStar650CL

How often can you use Cataclean?
I recently used a gallon of Lacquer Thinner poured in a half tank and vehicle ('01 Path 2WD) seems to be running smoother since and the single Bank 2 P0430 code hasn't come back (yet). But I'm wondering if it's only a matter of cleaning Cats or if they just eventually die. (105K)

You also mentioned that a 2WD Cat replacement is DIY doable. I looked at mine a while back and saw how extensions could fit up there except, even though my Path is from a fair climate, the rusted bolts look formidable. Are those bolts pressed in or do they come out? I.e. - to save some time I was thinking I could maybe grind/shear some nuts/bolts off(?) & punch out the cut bolt(s). Any experience / tips you could share on removal?

CAT Bank 2 - https://imgur.com/a/QvLqTOx

You guys mentioned there are more than 2 Cats ?! I was going to theft-protect what I originally thought were the cats (next in line downstream) until I learned that the Cats are the ones up stream sitting diagonal. Are those others downstream Cats too?!

----------------------------------------
*(edit) - Just dawned on me that it might be possible to get a sawsall blade in there and cut the bulk/body of the Cat out of the way to more easily address the rusted bolts (?)

Pathyj1 wrote: ↑

Tue Jan 03, 2023 2:11 pm

VStar650CL wrote: ↑

Tue Jan 03, 2023 10:41 am

DIY-able if you have good tools and good skills… My go-to is usually AP/Eastern Catalytic, decent price, good quality, and (very importantly) they usually fit right without any screwing around.

Thank you @VStar650CL.

I apologize for being high maintenance. Although I’ve done a wide variety of repairs on my multiple cars that are 20+ years old, this is actually my first time running into a catalytic converter issue.

I’m not sure what I have to buy. I’m in California so I know there are specific models for us. But there are some that are for the front vs. the rear, while some have additional tubes attached, and there seem to be gaskets and clamps involved.

Might someone be willing to provide a little more detail about what I need for my California 2001 4wd Pathfinder? And where would be the best websites to buy them?

I you are buying in for California - they must have the CARB on them or else they will not install them. Ensure that they do not need addition al hardware like my 97 SE 4x4 does. I got a quote at a shop (before pandemic and thefts of catalytic) I got the price of $1,200 for both. I decided to pause it since I really did not needed them. The guy told me that he would have to drop the lines and then install them back.