2006 Pathfinder P0420 DTC with exhaust leak

[Bluestream]

Geting a P0420 (bank 1 catalyst below thresthold) This vehicle has O2 sensor ( AR sensor) sensor 1 is right behind the exhaust manifold, then the primary cat, then sensor 2 behind that cat. Has a secondary cat, then a pipe into the muffer. I have a small exhaust leak behind the secondary cat. (well back from sensor 2) would this leak casue a 0420 code being so far back and behind the second cat?

TIA

 

[dumkid]

No but a tired 02 sensor or bad wiring can cause this code

 

[slacktide_bitog]

In that setup, only the primary cat is being monitored. A leak that far after the cat, after the last oxygen sensor, will not trip the P0420.

You need a new primary cat, and you should replace the o2 sensors along with it. While the hole isn't the cause of the code, you should still get a new exhaust. If you're lucky, somebody will make one from 304 stainless.

What kind of car is it for?

 

[Bluestream]

Both front O2 sensors are new, the muffer is one year old and the flange on the rear cat, and the flange on the muffer are not a perfect fit, as the gasket has worn out on the bottom over the past year from exhaust gas blowing by. A tiny leak I would say. I have susupected the primary cat, as they are weak on these models. Both rear sensors seem to have very similar voltage when I monitor on my scanner. I don't think the rear O2 is defective.

Not sure why the secondary cat is even needed?

 

[slacktide_bitog]

Both front O2 sensors are new, the muffer is one year old and the flange on the rear cat, and the flange on the muffer are not a perfect fit, as the gasket has worn out on the bottom over the past year from exhaust gas blowing by. A tiny leak I would say. I have susupected the primary cat, as they are weak on these models. Both rear sensors seem to have very similar voltage when I monitor on my scanner. I don't think the rear O2 is defective.

Not sure why the secondary cat is even needed?

An exhaust gasket should last more than a year. If it was installed by a shop, they should've welded it or something. Regardless, an exhaust leak after the cat will not trigger the code.

If the car is in reasonably good shape, not too rusty, and the car is worth keeping, get a California-legal cat, even if Canada doesn't follow California emissions. The CARB cats have more precious metals in them and last longer. Otherwise, Rock Auto has the "original performance" brand that is black coated, so it should last longer before it rusts.

As for the secondary cat that isn't monitored, I have no idea! Just replace it when it rusts.

 

[Bluestream]

I plan to buy a locally made CAT, they are $99 CAD. No idea if they are CARB, not I guess not. The truck is in great shape, but we are talking 18 years old, and I use it mostly for winter. I would just skip replacing it, but I read the porcelain can crumble, and get sucked up into the engine. When I installed the muffler, the flanges did not mate perfect. I heated them with acetylene and banged them true, and when I bolted them together they seems fine and had no leak. I assume they were not tight enough, and part of the gasket wore thin. An easy fix

 

[Bluestream]

Link to CAT

 

[edyvw]

Both front O2 sensors are new, the muffer is one year old and the flange on the rear cat, and the flange on the muffer are not a perfect fit, as the gasket has worn out on the bottom over the past year from exhaust gas blowing by. A tiny leak I would say. I have susupected the primary cat, as they are weak on these models. Both rear sensors seem to have very similar voltage when I monitor on my scanner. I don't think the rear O2 is defective.

Not sure why the secondary cat is even needed?

OE? Bosch? Denso or?

 

[Bluestream]

OE? Bosch? Denso or?

NTK

 

[edyvw]

NTK

Hmm, that should not be an issue. Wondering if the leak is creating some issues with pressure.

 

[SC Maintenance]

If its the VQ40 version its the same setup as my Xterra and Fronty. The Nissan cats are well known for early failure.

I would make sure everything works well before replacing the cat - plugs, good fuel trims, etc. You don't want to burn up a new cat.

It could still be the rear sensor. The code is based on them cycling with enough frequency, not the absolute voltage. Its says what that is in the manual - I want to say its one full cycle - low to high then back to low - in under 5 seconds going from memory. In the end its likely the cat, but you might want to try the sensor anyway - there only around $75 from RA. You want to stick with NTK or Denso on these.

The rear cats are not monitored. I presume they were put there to meet the CARB compliant state requirements but that is guess. However without them they are quite a bit louder according to the forums.

 

[Bluestream]

Well, I do have a spare rear O2 never installed its a API brand (China) I may as well install it and see.

Also, I have been getting different readings from my 2 front O2s' This was the case with my old sensors, and the issue carried over to the new sensors. Bank 1 voltage is always about 2x bank 2. I'm not sure which is correct, or how to troubleshoot, all spark plugs are in good shape. Maybe an injector issue, but plug color is all good?

 

[Bluestream]

So changing the rear o2 seems to have fixed this code. I would not have believed it, but here we are.