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Discussion Starter #1
Hi,

My 2006 Xterra has a P0420 error code. Below is my OBDII results:

Bank1:
  • Is my upstream sensor bad, as it's holding at 0.3V
Bank2:
  • What is going on with both of these O2 sensors? Upstream is holding slightly rich, and downstream is moving around?
 

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Hi,

My 2006 Xterra has a P0420 error code. Below is my OBDII results:

Bank1:
  • Is my upstream sensor bad, as it's holding at 0.3V
Bank2:
  • What is going on with both of these O2 sensors? Upstream is holding slightly rich, and downstream is moving around?

Upstream sensor is air/fuel, downstream is o2 for reference. It looks like your cats are bad, the post cat sensors are all over the place and they should be mostly steady when in closed loop.
 

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Discussion Starter #3
Upstream sensor is air/fuel, downstream is o2 for reference. It looks like your cats are bad, the post cat sensors are all over the place and they should be mostly steady when in closed loop.
Why are the upstream sensors holding a steady voltage? I thought they always fluctuate voltage up and down. Both banks #1 and #2 show an upstream sensor that is holding steady. Bank #1 upstream is running lean, and Bank #2 upstream is running rich?


Thanks,

Mike
 

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Hi Mike,

When at cruising (partial throttle, steady load) on these the B1S1 should hang out around .3V and B2S1 hangs out around .6 V. They are offset. The B1S2 switching frequently is indicative of a bad bank 1 primary cat and is the reason the P0420 code is setting. After you replace the cat, you will find the B1S2 voltage holds more steady.

Please see this thread I started and see post#2 watch the videos, the will show you exactly what you are seeing.

https://www.thenewx.org/forum/11-powertrain-driveline/217617-replacement-cat-converter-choice-tracking-feedback-discussion-re-p0420-p0430.html

Time for new cats. I’d recommend replacing both primaries when you tear it apart as when one goes the other is usually not long from also failing. Making maters more urgent, when these go really bad they can break apart internally and be sucked back into the engine destroying it. It’s happened to several members. I think even right now there are 2-3 people on here going through engine replacements because of failed cats.
 

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Here is a copy/paste of the post I referenced

For those curious what it looks like when you have a cat going bad. The following is an excerpt from the FSM:


DTC P0420, P0430 THREE WAY CATALYST FUNCTION
On Board Diagnosis Logic

The ECM monitors the switching frequency ratio of air fuel ratio (A/F) sensor 1 and heated oxygen sensor 2. A three way catalyst (manifold) with high oxygen storage capacity will indicate a low switching frequency of heated oxygen sensor 2. As oxygen storage capacity decreases, the heated oxygen sensor 2 switching frequency will increase. When the frequency ratio of air fuel ratio (A/F) sensor 1 and heated oxygen sensor 2 approaches a specified limit value, the three way catalyst (manifold) malfunction is diagnosed.


This video shows my B2 O2 S2 sensor high switching frequency indicating low oxygen storage thus setting a code for cat converter efficiency below threshold. In this case bank 2 (P0430) If you watch the botom right (B2 O2S2) you will see it switching way low to high. Compare that to B1 O2S2 at the bottom left which is much more consisitant.

The typical average values should be about:
B1 O2S1 ~0.3V, B2 O2S1 ~0.6V
B1 O2S2 ~0.6-0.7V, B2 O2S2 ~0.6-0.7V

Heres the vid:

Before (bad fluctuating B2 O2 S2 voltage):


After (good steady B2 O2 S2 voltage):


Hopefully this will help others in their diagnosis and understanding of what the ECM is looking for to trigger a P0420 (Bank 1) or P0430 (Bank 2) Catalytic Converter Efficiency Below Threshold code.

FWIW, at the time of this "Before" video mine has reached the point it will set the code within 100-200 miles after clearing. In fact it set only 30 miles after I cleared it.

Something else to consider and examine: Look at your Long Term Fuel Trims. If you see one side is way low, this will indicate it is taking away fule on that side because it is running rich. And if way high its adding fuel because the enine is running lean. This indicates a problem other than just age that is causing the cat to fail. In my case both banks are the same and normal. Thus indicating the converter has simply began to fail and run out of oxygen storage. ymmv

-Jay
 

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Discussion Starter #6
Thanks. Very helpful. After reading through all 19 pages, there no1 seamed to find a California legal cat.

What about this one for my bank1: hottexhaust.com/Magnaflow_558668
 

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Discussion Starter #9
This. They cost more but most of the aftermarket ones are so hit or miss with quality they still throw a code. At least with OEM you can replace it and be done.
Thanks for the feedback.

The dealer cats are 800 + core = $1000

Online is was <$400. I am going to do some research. $600 savings is a lot.
 

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If you live here in California they have us by the balls man


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Best case you get a lax smog guy who just looks to see if they are there.

Worst you get a guy who takes it serious and you buy two sets of cats to pass smog.


That’s not withstanding the seemingly lower span of life from the aftermarket offerings. Like a lot of things on our truck oem just seems to be he best choice. I’m all for the economical route. Post your experiences in the aftermarket cat thread for the data collection and collective betterment of us all. :)


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This. They cost more but most of the aftermarket ones are so hit or miss with quality they still throw a code. At least with OEM you can replace it and be done.
Thanks for the feedback.

The dealer cats are 800 + core = $1000

Online is was <$400. I am going to do some research. $600 savings is a lot.
As an alternative, Magnaflow makes California legal bolt on converters for about half the cost of OEM. I installed a set 3 months ago on the Frontier. Did have to buy new ring gaskets for the flanges and bend the manifold heat shields a little bit so they would clear the O2 bungs. Apart from that they work fine and passed CA smog no problem.
 

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So I guess my question is what is actually happening here? My 06 that I just gutted the cats on and used spacers for the downstream o2s also has a steady upstream .3 and .6 volt readout which seems to be hybrid/anomaly of some sort that other xterra, frontier and pathfinder owners have reported also having. All I have ever seen is either the standard switching .1-.8 volt o2 or the newer wide bands which use a much higher voltage or display on mA I believe. I know using he same obd2 scanner between my two xterra shows my 06 to have the steady .3/.6 but my ‘11 pro4x shows that it is using a/f widebands. So why is it that our x’s do this? Technically the average of those two numbers is .45 volts which is what they say upstream should average out to but that is when they are switching. It’s supposed to be an average for the bank, not an average between the banks. This also made me question my understanding of what triggered a p0420/30. I thought the ecu was looking for a minimum difference between the upstream average and the downstream constant. Meaning it was increasing the amount of o2 in the downstream by a specific percent. Which would mean the downstream would fluctuate too but once I learned downstreams are supposed to be steady to indicate a working cat it makes me think that it looks for a certain target downstream rate meaning no matter what goes in a specific mixture comes out. Even if the downstream volts are higher than the upstreams, which is the case of the .3volt upstream bank. I am getting both p0420/30 codes even with the spacers and my values up and down match each other which makes sense as the spacer still allows full access of the exhaust gasses to the sensor tip. So the spacers really do nothing. Someone please help me understand all this as the upstream values and what triggers the p0420/30 has now got me all tirned around.
 

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Anyone have any additional insight? Would love to hear from those more in the know.
So I guess my question is what is actually happening here? My 06 that I just gutted the cats on and used spacers for the downstream o2s also has a steady upstream .3 and .6 volt readout which seems to be hybrid/anomaly of some sort that other xterra, frontier and pathfinder owners have reported also having. All I have ever seen is either the standard switching .1-.8 volt o2 or the newer wide bands which use a much higher voltage or display on mA I believe. I know using he same obd2 scanner between my two xterra shows my 06 to have the steady .3/.6 but my ‘11 pro4x shows that it is using a/f widebands. So why is it that our x’s do this? Technically the average of those two numbers is .45 volts which is what they say upstream should average out to but that is when they are switching. It’s supposed to be an average for the bank, not an average between the banks. This also made me question my understanding of what triggered a p0420/30. I thought the ecu was looking for a minimum difference between the upstream average and the downstream constant. Meaning it was increasing the amount of o2 in the downstream by a specific percent. Which would mean the downstream would fluctuate too but once I learned downstreams are supposed to be steady to indicate a working cat it makes me think that it looks for a certain target downstream rate meaning no matter what goes in a specific mixture comes out. Even if the downstream volts are higher than the upstreams, which is the case of the .3volt upstream bank. I am getting both p0420/30 codes even with the spacers and my values up and down match each other which makes sense as the spacer still allows full access of the exhaust gasses to the sensor tip. So the spacers really do nothing. Someone please help me understand all this as the upstream values and what triggers the p0420/30 has now got me all tirned around.
 

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This is where I got my CA compliant cats, Rockauto.com, 11/29/2018:

WALKER 31576 Pipe Flange Gasket / Seal $ 1.92 $ 0.00 2 $ 3.84 (Header to CAT gasket, bought two to have a spare)
WALKER 31540 Pipe Flange Gasket / Seal $ 1.30 $ 0.00 1 $ 1.30 (Already had two, bought another for a spare)
2006 NISSAN XTERRA 4.0L V6
Left (Driver) side cats and sensors: Looks like the links just take you to the generic page. They are on it.
BOSCH 17204 Oxygen (O2) Sensor $ 77.89 $ 0.00 1 $ 77.89 http://www.rockauto.com/?carcode=1433009&parttype=5132
BOSCH 16513 Oxygen (O2) Sensor $ 72.79 $ 0.00 1 $ 72.79 http://www.rockauto.com/?carcode=1433009&parttype=5132
WALKER 83698 Catalytic Converter $ 246.99 $ 0.00 1 $ 246.99 http://www.rockauto.com/?carcode=1433009&parttype=5808
WALKER 83892 Catalytic Converter $ 255.79 $ 0.00 1 $ 255.79 http://www.rockauto.com/?carcode=1433009&parttype=5808
Shipping Ground $ 11.99
Order Total $ 670.59

If doing the job yourself put a high temp sealant/gasket maker on the gasket between the two cats. I had to pull my second cat off and put it on as either the gasket is to flimsy or the pressure to great for the gasket and destroyed the gasket. Good thing I bought a spare. I was getting a Air/fuel code after clearing the CAT code.
 

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HI! do you happened to know the part # for the cats from magna flow that you bought. And other parts I should need. I'd appreciate it. Thanks.

Sent from my SM-N910T using Tapatalk
 

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As an alternative, Magnaflow makes California legal bolt on converters for about half the cost of OEM. I installed a set 3 months ago on the Frontier. Did have to buy new ring gaskets for the flanges and bend the manifold heat shields a little bit so they would clear the O2 bungs. Apart from that they work fine and passed CA smog no problem.
HI! do you happened to know the part # for the cats from magna flow that you bought. And other parts I should need. I'd appreciate it. Thanks.

Sent from my SM-N910T using Tapatalk
 
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