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Discussion Starter #1 (Edited)
**UPDATE**
Long story short, I ended up replacing both of my cats and the rest of the exhaust system with it. My mpg is now consistently significantly better too.

While the codes were gone for a long time, they started to come back about once a month. Upon further investigation, i found my ScanGauge II was fairly often reporting a pending P0430 or P0420 code. Nissan refers to this as the first trip diagnostic trouble code (DTC). The check engine light will not come on until it gets the same code code on the next consecutive trip. With the new oxygen sensors, it seemed that I was getting the pending code during my morning drive to work, but during the evening drive, the code would clear. So I was rarely getting a check engine light, but the problem still existed. I also did the diagnostic stuff in the factory service manual for this code. Checked the spark plug coil packs, replace the spark plugs while I was in there. I even went as far as taking out the fuel injectors and to check and cleaning them. However, nothing changed.

I was also able to program my Scangauge II with xgauges to monitor the sensors. At a steady load around 2000 rpm driving down the highway, the sensors would report
Bank 1 - Sensor 1 (pre cat): 30 and stable
Bank 1 - Sensor 2 (post cat): 50-60, but would often jump to 10s, and then back up to 50-60
Bank 2 - Sensor 1 (pre cat): 60 and stable
Bank 2 - Sensor 2 (post cat): 50-60, but would often jump to 10s, and then back up to 50-60
http://www.scangauge.com/support/x-gauge/xgauges-for-iso-vpw-vehicles/

After replacing the cats, I am now getting
Bank 1 - Sensor 1 (pre cat): 30 and stable
Bank 1 - Sensor 2 (post cat): 70s and stable (no more jumps)
Bank 2 - Sensor 1 (pre cat): 60 and stable
Bank 2 - Sensor 2 (post cat): 70s and stable (no more jumps)

I am just glad to be done with it, as I was tired of getting the codes. I am also pretty sure that my MPG would take a hit. I was getting between 14-16 mpg when there was a pending or active P0430 or P0420 code. Now, every day after having the new cats, I have been getting 18-20 mpg.

I was originally under the belief that the catalytic material should not wear out under normal use. However, the aftermarket folks saying that the reason their cats are smaller than the OEM ones is because they are only required to last 25k miles instead of the OEM 80k miles, so they don't put as much material inside their cats. Apparently Nissan just doesn't build their cats to last much longer than 100k miles and that this just needs to be done.

Sorry if I gave anyone false hope. I would still recommend replacing the sensors at the same time or as a last resort before you actually replace the cats in case you do have a bad sensor. But is seems that if you are getting the code, it most likely does mean you will be needing to replace your cat(s).

Installation Notes if you plan on doing it yourself:
* Make sure you are using 6 point sockets and wrenches. Otherwise, you will be sure to round some bolts out.

* You need to unbolt the manifold heat shields, but they don't need to be removed or cut out like i have read some have done. It can be slid forward far enough to get a flat wrench in there to removed the top two bolts on the cat. For the bottom bolt, there is enough room on the drivers side to get a 1/4 inch ratchet with a deep 14mm socket. On the passenger side bottom bolt, there is just enough room for a 3/8 inch ratchet and a 14mm deep socket. Many have said they have had problems with the heat shield bolts breaking off. Mine looked pretty bad, but still came out easily. I replace them with new ones and slathered them with anti-seize.

* There is one stud on the exhaust manifold, and two studs on the cat. Loosen the bolt on the stud of the exhaust manifold (on both sides) first using some PB-blaster. If this stud breaks, you need to stop and re-evaluate. Getting that stud out might involve drilling, or whatnot. If the studs on the cat break off, you will probably need new nuts, but otherwise, it isn't a big deal. After 160k miles and many new england winters, mine were not that rusted, I assume because they are up far enough in the engine.

* Make sure you get new gaskets. Between the manifold and the cat, there is a metal ring crush gasket that fits snugly around the pipe in the flange. As you tighten, it crushes to form the seal.

*Depending on how rusty the rest of your system is, you might want to plan to replace everything. My bolts between the primary and secondary cats came out pretty easily despite being rusted to hell and back, but the bolts between my secondary cats and the muffler pipes rounded off. Instead of messing with them, i just hack sawed them out.

*Be prepared to explain to your friends that you are not hurting yourself by cutting up your hands. I have a good number of cuts and scratches. The head shields under there are sharp.

**************************************************Original Post*******************************************************************************
I posted this in an older thread, but I decided it might be worth making into a new thread.

In short, just replacing my upstream and downstream oxygen sensors on the drivers side of my 2006 cleared my P0430 code that I have been getting very often for about a year. Over the winter, i was getting the code every day, but it has been gone for about a month now.

Specs:
Year: 2006 Xterra S
Miles: 164,000
All Original Exhaust

(In more detail...)
I have done a lot of reading on this site and other sites about the P0420 and P0430 codes, and I don't recall anyone saying that they tried just replacing the o2 sensor for this code to see if it would resolve the code. The Nissan FSM doesn't even list the oxygen sensor as a possible cause of this code.

Obviously, this will not work for everyone. If there is something wrong with an engine and the cat is coated with carbon from running too rich, or the cat is physically damaged, then this won't help you. This is also a 2006 ECM. It is possible that newer ECMs have different firmware that might report things differently, but I kind of doubt it.

Over the time I have been getting that code, my MPG has been about the same and the engine runs fine (no stalling or loss of power). In the summer when it was hot outside, the code would happen less often, maybe once every two weeks. But when it was cold, it happened daily. (I always cleared the code with my Scangauge II to keep track of how often it happened). One thing I noticed with my Scangauge II that even in the bitterest of cold, like 5 degree F mornings, the ECM would go into closed loop mode within 5 or 10 seconds of starting the engine which I thought was a little odd.

With the new O2 sensors, I have noticed my MPG go up by around 2. (I am not really sure if it ever made my car be in "limp" mode due to the code, but maybe). This morning when it was 15 degrees F, the car stayed in open loop mode for about 2 min.

I have avoided doing anything about the code for so long because everything I read and people I asked always said "If you get this code, you HAVE to replace the cat. It is not the o2 sensors, they have their own code" and I was not looking forward to the prospect of dropping my 7 year old rusty exhaust to do this. After this experience, I will probably start replacing my O2 sensors every 100k miles at least. They are pretty easy to replace too. Downstreams have easy access from under, and the upstreams, you just have to take off the front wheels and move the plastic aside (though it might be a little easier to just remove the wheel well plastic).

Alltrade 94800 O2 Socket Kit: (Straight one was good for the upstreams, but the crows foot was better for the downstreams)
http://www.amazon.com/gp/product/B005SMUORO
ACDelco 213-3896 Professional Heated Oxygen Sensor, Position 1 (x2)
http://www.amazon.com/gp/product/B000JZZBKK
ACDelco 213-3117 Professional Heated Oxygen Sensor, Position 3 (Downstream Passenger side)
http://www.amazon.com/gp/product/B000EQRRDS
ACDelco 213-3066 Professional Heated Oxygen Sensor, Position 3 (Downstream Drivers side)
http://www.amazon.com/gp/product/B000EQPACS
(They all come with Anti-seize lubricant)

Sorry for the book long post, but this is about a years worth of on and off research and thinking that I wanted to get out there to maybe help someone else not replace a catalytic converter that doesn't need to. Besides, if you are going through all the trouble to replace your cat, it can't hurt to replace the sensors too. If this doesn't work, you at least already have the new sensors. And if you think about it, what makes more sense, a group of corrosion resistant metals "wearing out" or a sensor that creates voltage from a molecular gradient through ceramic that also has an electronic heater and has an external air port (in the wire harness that could get clogged with dirt) "wearing out"?

Please send along any experiences you have had regarding your oxygen sensors and these engine codes. Has anyone with original cats and either of these codes replaced their oxygen sensors and had their codes come back in a short time?

If my P0430 code comes back, I will be sure to update this post.
 

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Discussion Starter #3 (Edited)
for those of us who did not know, you dont want to erase the code with the engine running-its bad for the ecu
I have heard this before, but I have never seen any good evidence to back it up, at least in modern engines. Blanket statements like this always make me uncomfortable (like "the o2 sensors have their own engine code when they go bad"). It probably isn't best to clear an engine misfire code, but something like emissions can't be that bad.

Do you have any good links that talk more to this?

I feel like the idea of this problem probably stemmed more from old engine computers in certain makes and models that were not programmed well enough to realize a problem it is compensating for still exists even if the code is cleared while it is running and goes on to damage the engine.
 

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Discussion Starter #7
What was your mileage before and what has it improved to? How many miles are on your 06?
Posted via Mobile Device
I have about 164k miles. My commute in the cold with the winter blend fuel has been about 14 mpg all winter. It is now back up to 16 which is what I feel it use to be.


Any reason why you went with AC Delco, Instead of Denso O2 Sensors?
I saw one reference on these forums to Denso being the likely Nissan OEM, but I have not found any other references to that on the internet. I have a few friends that have had poor luck with Bosch, but good luck with AC Delco, so I went with them. The cables were a little longer, but they looked identical. Parts always have the disclaimer anyway "This product is in a Denso package, however the part may have been manufactured by an independent Denso supplier. " so whatever you get probably isn't exactly oem anyway.
 

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Very interesting because I started getting that code a couple of months ago. I used my $20 scanner to pull the code and then went to Nissan that same day to ask about the possibility that it might be a false code (I hadn't researched anything up to that point).
The service tech told me that the cat needed to be replaced and that it was cut and dry.
I went away pondering the cost of the repair and then did some research that I had to replace with OEM catalytic converter or the ECM would just keep throwing codes and it wouldn't pass inspection. I cleared the code and the next day went back and talked to the guy at the service desk who I dealt with when they replaced my transmission (2005 SE). I knew that he was a straight shooter. Anyway, he said that the condensation w/ the sudden drop in temperature could cause the code (the weather fit that scenario). My X threw the code one more time about a week after, but it has been a month since the list time it did it.
The one thing I did read was that there was no way in hell that replacing the O2 sensors would work and that the reverse would be true (if your sensors were bad, they wouldn't signal that the cats were bad).
Anyway, I'm code free for now.
I just blew a grand on an a transfer case acctuator that I don’t' think needed to be replaced, since they had to do more troubleshooting after replacing to finally figure out that it was a solenoid with a bugged up connection. They said the acctuator was bad also (leaking). I asked for the part and have it, but no way of knowing if it is still good or not.
So, the P0430 code that happened a week later didn't make my mood too sunny.
I'd have said AC Delco would have been my LAST choice for any part, but reading the one objective study on air filters, where they were at the top on every attribute (filtration, efficiency, etc), I’ve used their filter ever since (a1267c for those interested in the model). Who knows where the 02 sensors were made, but I’d choose the AC Delco based just on the air filter.

Dave
 

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Discussion Starter #9
I'd have said AC Delco would have been my LAST choice for any part, but reading the one objective study on air filters, where they were at the top on every attribute (filtration, efficiency, etc), I’ve used their filter ever since (a1267c for those interested in the model). Who knows where the 02 sensors were made, but I’d choose the AC Delco based just on the air filter.

Dave
I too have read that air filter study and have been using the AC Delco air filter, but AC Delco still wasn't at the top of my list when I started to research oxygen sensors. But I am still happy so far with both of them.

I hope it was a fluke, and you remain code free. Can I ask how much the dealer quoted you to replace the cat? I have seen wildly different numbers from different people.
 

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Discussion Starter #10
UPDATE:
Long story short, I ended up replacing both of my cats and the rest of the exhaust system with it. I edited my first post with the details that lead to making this decision.
 

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Anyone know of something to get rid of the Pa200 code? I've replaced both my primary cats, (the drivers side twice) and the passenger forward O2 sensor. The O2 code comes back all the time. I've replaced it with a new Bosch, and code just keeps coming back.



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Discussion Starter #16
Forgot to mention that. I have too heard of other car makes having issues with BOSCH sensors. A friend that I know had a problem with bosch replacement, switch to AC delco and didn't have a problem after that. Many on the forums swear by Denso as they are probably the OEM Japanese Nissan manufacturer.
 

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I bought it at Autozone.

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Uh oh, I inquired at autozone once and they were trying to sell me one of those cheap universal ones for my upstream, and I told him that it's not right for the upstream but according to him his computer knows best.

I'd order some Denso Upstream Sensors.

http://www.amazon.com/Denso-234-5060-Fuel-Ratio-Sensor/dp/B001F7CG04/ref=au_pf_ss_11?ie=UTF8&Make=Nissan|67&Model=Xterra|901&Year=2006|2006&carId=003&n=15684181&s=automotive
 

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It wasn't cheap. In fact I ordered a Bosch from Rock Auto first, but ordered the wrong one by mistake. I was in a hurry to want to get it all done so I went to Azone. It worked great for over 2 weeks. Then the same code came back. Now it comes back on the same day I reset it with the Super Chips.

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+1

So now I'm getting this code too (P2A00).

Both O2 sensors on the passenger side are OEM.
I've cleaned (not replaced) the MAF sensor, looked for intake leaks, and I know there are more possible causes.

Has anyone identified the fix for a P2A00 they experienced?
 
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