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2006 Nissan Pathfinder: I'm replacing left/right forward catalytic converters

Trying to get my facts straight before I remove the old cats and replace them with Walker brand parts.

Difficult to access the nuts/bolts and O2 sensors due to confined workspace.

  1. It looks like the foward flange is loosened by removing two nuts from the manifold side of the flange, and the third nut from the exhaust side. Is that correct? All nuts are 14mm, yes? Any tricks on gaining access to the forward flange nuts? Or any tool tips?
  2. On the rear flange of the old forward cats, the flange was threaded with two studs which were nutted from the exhaust side. However the rear flange on the new Walker cats are not threaded… just slotted. So, will any stainless bolt/nut work as a replacement there?
  3. O2 sensor takes a 22mm open wrench, yes?


Hold your horses . . .

WHY are you planning to replace both catalytic converters?

Who told you they need to be replaced?

Are they literally rusted out? This is doubtful, because cats have been stainless steel for some time now

Has the monolith broken free of the shell on both of them?

Did you bottom out, causing massive physical damage to the cats?

Cats often fail as the result of something else . . .

Severe misfires
Leaking fuel injectors
Excessive oil consumption
Extremely rich mixture

Does any of this sound familiar?

Why? showing both 0420 and 0430 codes on OBD-II. Can’t/won’t pass emmissions and would prefer to not have my vehicle registration suspended in the next 30 days.

Why not? I have the new cats. I have access to shop and tools. I got skillz. :slight_smile:

Other stuff sounds familliar, but is not the problem. Car runs excellent. No leaks, no squeeks, no smoke. No symptoms of ANY problems… other than OBD-II. Maryland WILL NOT pass my car until OBD runs clear after seven days of driving. Simple reset won’t work. Codes reappear within 2 days.


It has sometimes been the case that degraded oxygen sensors cause P0420 and P0430

There have even been instances where PCM software which is too sensitive causes P0420 and P0430

Replacing the cats might indeed allow you to pass emissions, but if the problem is actually a mixture problem, the new cats will be quickly ruined and the codes will re-appear. But you will probably have passed emissions, so there’s that. It’s sort of unusual for a 2006 vehicle to need two new cats, let along one new cat. How many miles do you have on it? Any drivability symptoms? Or is the only problem the CEL and associated codes?

That was my first thought, as the same thing occured with my MX-6 a few years ago. Replacing the O2 sensors cleared the CEL, but also led me to say “what the hell, let’s see what else I can do with this thing” and replace the entire exhaust system from headers to tailpipe. I learned a lot and it motivated me. I have a pair of replacement O2 sensors for the Pathfinder cats, as well. As with the Mazda, I debated replacing the entire exhaust system, as well, but chose to only replace the forward cats at this time.

160,000 miles. NO symptoms. Just the codes, and state emissions inpsectors that won’t bother to shove the probe up the tailpipe do a real analysis when they can just read your OBD and fail you.

I appreciate the sanity check guys, but can someone address my original questions? Especially, #1. The forward cats are a b!*ch to get to. If you have personal experience working on a Pathfinder exhaust, do you have recommended method for getting at the bolts on the foward flange? Is it easier to come in from the engine compartment side? Do I need to remove the plastic wheel well covers? Some other clever method? That’s all I’m asking. Thanks!

Replacing the O2 sensors cleared the CEL, but also led me to say "what the hell, let's see what else I can do with this thing" and replace the entire exhaust system from headers to tailpipe.

Catalytic converters usually last the life of the vehicle. I think it’s foolish to replace a very expensive part that in all likelihood doesn’t need replacing. Most of the time it’s an O2 sensor. I’d just replace that.

OP has already bought and paid for the cats. They’re apparently in his possession, waiting to be installed. It’s going to happen

@barkster … haven’t ever worked on a Nissan, just a DIY’er myself. Did a little research, can’t vouch for this info, but might be of some help anyway. 06 Pathfinder V6-4 L 2WD.

Remove in this order: protector, em cover bolt, center tube, muffler, front tube, O2 sensor wire, cat nuts, O2 sensor. Look in the FSM or equiv for specific tools and torques spec requirements for the O2 sensor. Not torqueing the O2 sensor correctly can apparently cause the CEL to come on.

@george … thanks. You are correct to point out having proper instructions. When I did this on my Mazda, I had the benefit of the FSM. Not so this time, having looked at my Nissan’s undercarriage for the first time for anything beyond changing the oil/filter. I figured it might be a case of removing 10 things to get to 1, but I also had hope it would be simpe and easy. :frowning:
I’ll see if I can get a copy before this weekend.

Some manufacturers will allow you to view the FSM via the internet for a day or two, up to a week sometimes, either for free, or for a small fee. That’s one option maybe.

So, are you telling me I paid $150 each to replace 2 catalytic converters on my 2006 Nissan unnecessarily after the O2 sensors had already been replaced, it threw a 0420 code and was running like it was going to shut off any moment?

I couldn’t tell you with authority if the new cats were necessary or not. But if your truck “was running like it was going to shut off any moment,” I would certainly say you had a bigger problem brewing than I did (with just the CEL codes coming up and no other symptoms).

Based only on your brief description, I would lean toward “they were probably necessary”. Or at least they were definitely worth investigating.

Nobody has offered an opinion about your vehicle, you should repair your poorly running engine before damage to the catalytic converters occurs.

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Yes… as @Nevada_545 correctly points out, I should clarify my previous post.

I would say you may have needed to replace them… not so much as the cause of your engine problem… but more likely as a result of your engine problem.

This is another one from 2014. Sorry Nevada, there was absolutely no date when I clicked on it. How are we supposed to know its old?

My screen has a timeline sort of thing on the right hand side. The top of it says “March 2014” on this thread.

Yeah once you click on it, but until you open it up there is no date-on my computer anyway that I’ve seen.

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On the main page, to the right, under the heading Activity, hold your cursor over the last time that someone responded to the post, and it will show the date of the original post.


Personally, I wouldn’t even try to remove the O2 sensors; I’d just replace them as part of the project. Generally by the time the cats become inefficient, the same accumulated deposition that caused them to be so is also present on the upstream O2 sensors sufficient to affect them too. If you reuse them, you’ll probably be back under the vehicle six months from now.

I commend your going through this in your mind and asking questions before proceeding. You sound quite capable, perhaps only feeling a touch of preproject anxiety. I get that too.

Let us know how you make out. We do care.