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Discussion Starter · #1 · (Edited)
Code says: "Catalyst System Efficiency Below Threshold (Bank 2)"
Now... I want to replace the O2 sensor downstream of that cat but... I see "left" and "right" O2 sensor.
Which is Bank 2? L or R?
Are the connectors and harness the same? I want to swap the O2 first...
 

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Bank 2 is the front one. Replacing the downstream sensor will do nothing, replace the upstream one first. If the upstream sensor doesn't fix it, you need a new cat.
 

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Discussion Starter · #4 · (Edited)
Thanks for info!

I was thinking that, if it is the O2 sensor, it would be the downstream one that mesures the cat eficacity. Engine runs great - it would not if it was the upstream one, no?
Downstream ones are harder to reach from the driveway :)

It is an annoynace for a year now, luckly we don't have emisions tests here. I have 176k miles, true, but if it is the cat, why... just that one? Hmm...
 

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No, the upstream sensor monitors and controls the air/fuel mixture, and if it goes, it will adversely effect the performance of the converter, and if ignored, can permanently damage it. The downstream sensor is protected by such things because it is behind the cat, so the only thing that can damage the downstream sensor is an incorrect fuel air mixture, which would damage the cat first. If you had a bad downstream O2 sensor, you would have a code for a bad downstream sensor, not a converter code. This is why the upstream sensors are considered maintenance items, and should be replaced every 80,000 - 100,000 miles. If the upstream sensor fails, damage to the converter is the first consequence, and no, and incorrect mixture will not likely be noticed as a drivability issue, even though it can be bad enough to damage the converter.

Trust me, you need to replace the upstream sensor. If you are lucky, the code will go away and stay away. If it does not, your cat is toast and needs to be replaced.

To answer why only the one cat? Because the 2 banks of your car are individually managed, the problem is isolated to that bank. That cat is the one that is suffering because the sensor on that bank is not performing properly.
 

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Sounds like it is relatively inexpensive to preemptively

replace the upstream sensors and protect your converters.

I am at 75K now and am considering replacing both upstream sensors on my 2001 OHV. Fortunately, they are the easier ones to replace rather then the downstream ones.
 

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Discussion Starter · #7 ·
Well, a little to late for me, I am at +170K :)
I will invest in some new O2 sensors for pre-cat... The radiator side one (the one with the code) looks to be in a decent position to remove. Don't know about the other one.
 

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Discussion Starter · #9 ·
What's new? :D
I was looking at the post-cat ones and I cannot see where the connectors are - wires are going somwhere in the same "favorite" location - by the firewall.
 

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How is your fuel economy? If it's OK and your fuel trims don't look bad I would just let it go. The 02 sensor on the firewall side is extremely difficult to change, and you may end up replacing them all only to find out you need catalytic converters.
 

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Data store

How is your fuel economy? If it's OK and your fuel trims don't look bad I would just let it go. The 02 sensor on the firewall side is extremely difficult to change, and you may end up replacing them all only to find out you need catalytic converters.
I would invest in a CarChip, let it gather the data and show me the charts. What if none are bad and you spend time and skinned knuckles for nothing?

Just my thoughts.

I put charts in the general catagory today.

-chart-
 

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Discussion Starter · #12 ·
OK, for P0430 code...
I replaced the associated O2 upstream sensor (the one by the radiator). Bosh 13117 for 30$ Amazon.
Code cleared and didn't show up yet. I even check the "pending codes" and is not there. So I hope that was it and not the expensive cat. If reapears I will post (full of sorrow) here.
 

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I assume your scan tool lets you check the status of IM monitors? If so, check to see if the cat efficiency monitor is complete. If cat efficiency is complete, you are good to go!!!!
 

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Discussion Starter · #14 ·
I don't have that smart of a scantool... It just shows the tripped and pending codes. I guess will know more tommorow after the comute.
 

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Discussion Starter · #15 ·
A few days in and no code. So I guess "Catalyst System Efficiency Below Threshold (Bank 2)" was actually related to a bad upstream O2 sensor in that bank.
Now, the engine idles so smooth, I can't belive what difference it made. I am almost tempted to replace also the Bank 1 O2 sensor, I am just scared of the accesibility.
The Bank 2 one (towards radiator) was unexpectedly easy - just a bunch of crud falling in my eyes from the traverse :)

Thanks everyone that piched in - Rep Powers to everybody :)
 
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