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Discussion Starter #1
I keep getting a bad cat code intermittently, so I am sure the catalytic converter needs replacing. For now I would like to replace both the up and down stream O2 sensors. My question is would a bad cat damage the O2 sensors? Should I replace the cat first and then do the sensors? It is a 2011 ex CRV. The code isP0420. The car also has 200k on it. Thanks.
 

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2006 EX AWD
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Autozone and the like would love to sell you O2s based on a P0420.
It won't fix your issue.
At 200+k, it's possible that your cat is worn out, it's also possible that something else is the root cause and replacing the cat will be a band-aid until your P0420 returns...
You can learn a lot from the STFT and LTFT.
 

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yes unburned gas wil destroy a converter so adjust valves and plugs if you replace the converter and any other codes ,an O2 spacer on the downstream O2 will keep the light off too (never put a spacer on the upstream O2 )
 

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Discussion Starter #5
Assuming it is the cat. If I want to replace it will an aftermarket OEM work or do I need to get the cat from the dealer? I live in NY.
 

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I don't understand one of the previous replies. O2 sensors can and do go bad. Why else would they sell them? Better to spend less on an O2 sensor than replace a cat that might not be bad. There are ways to test the O2 sensors. Keep in mind, too, that an OBD-II code only alerts you to an abnormality somewhere in that sensor's circuitry. You could have a corroded connector, a broken wire, a broken sensor, etc. that would trigger the error code. Everything between the ECU and the sensor needs to work properly, in other words. "Cat efficiency" only means that the ECU expects the value from the O2 sensor to be within a specific range. Whether that is caused by faulty circuitry, a bad sensor, or a bad cat can only be determined by testing. Not by throwing parts at it, in the hope that it will be fixed.

OEM or aftermarket cat, that's up to you. I used aftermarket in my '97 CR-V and it worked fine. But that engine is ancient technology, so I don't know if that would work as well for a third-gen CR-V. Use only Denso O2 sensor(s) if you find you need to replace. Others (especially the trash that Bosch makes) will not properly work on a Honda. Denso only.
 
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I don't understand one of the previous replies. O2 sensors can and do go bad. Why else would they sell them?
Yes, they do. However, the symptom presented is a P0420. Not the discrete code for either the upstream or downstream O2. Now maybe the OP didn't mention other codes that are present, in which case we wouldn't have all the information. Important to understand what a P0420 means.....If the cat is good, and the engine properly tuned the downstream O2 will switch very infrequently at a steady 2000rpm, while the upstream will be switching at least 5 times in 10 seconds (usually more like 15 times in 10 seconds). The ECU compares the switching frequency of the two sensors.... P0420 says the downstream O2 is switching almost as fast as the upstream....a sign that the cat is nearly depleted. I have no doubt that slapping a cat on will make the P0420 go away....at least for a while, depending on what else is broke.
To the OP, i could be wrong, but I think NYS has pretty strict standards and most aftermarket cats are not legal for sale in NYS. Doesn't mean it wouldn't work, you just might not pass inspection. A muffler shop if state certified would know for sure...
 

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It wasn't a CR-V, but I had the P0420 on my car and replacing the rear O2 sensor did indeed solve the P0420. Lasted for two more years before the P0420 came back and this time it was the cat just being dead after about 350K miles. After removing the cat to check to make sure it wasn't plugged up (it was squeaky clean and intact) I put a spacer on the rear O2 sensor and haven't worried about it since then. Car has 387K miles on it. Runs fine.
 

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Discussion Starter #10
yes unburned gas wil destroy a converter so adjust valves and plugs if you replace the converter and any other codes ,an O2 spacer on the downstream O2 will keep the light off too (never put a spacer on the upstream O2 )
Ok so I ordered a new Cat (discovered that it had Federal Emmissions). It came yesterday and there was no gaskets and bolts. I am new to this DIY car thing, so I assumed everything was there. Do you happen to know what else is needed or where I can find out? Did some Googling but got no where. Thanks in advance for your help.
 

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which converter did you get ,the first converter is the only one being monitored I think, if the 2nd O2 is between both converters anyway ,what I list in walker is 35129 spring bolts and 31673 gasket , the 16594 is the first converter
138341
 
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