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Discussion Starter #1
I see that it's a cat converter issue, but is there an easy way to tell which sensor it is? i may not be able to tell a difference looking at it
 

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P0420 isnt automatically a sensor. Nor does it mean one or the other is bad in every case. Can mean the converter is bad, there is an exhaust leak at or before the converter as well.

Now if it is indeed an O2 sensor issue, 9 out of 10 times it's the one after the converter.

The one in the converter it isnt an O2 sensor anyway, that is a fuel air ratio sensor and nothing but the proper one from denso will work correctly. Cant just put any O2 in for that one.

There is other things that can cause a 42p code as well. Dirty engine, valves out of adjustment, dirty injectors, worn spark plugs and so on can cause also cause it. P0420 isnt a code for the problem, it's a symptom of the actual problem.

I wouldn't put an O2 or converter in it just yet. Look at maintenance over the years make sure things are well past their due date for maintenance. Take care of those issues first. They are cheap and will.make your v run better, better mpg and all that. Reset the code and see if it comes back.

Also would be good to have a proper diagnostics done by someone who has a clue because they can see what the fuel air ratio, trims and such are all doing. This will show the issue if there is one. Having it properly diagnosed can also eliminate having to continue anything else as they can tell you exactly what's wrong.

If it does come back after all that then get an O2 extension (basically a spark plug fowler) which goes between the O2 and the pipe. Reset codes again. If it doesn't come back on for that code then likely your converter is wore out, which as long as it's not plugging up, I would just not worry about it.

After all that and it comes back on with the extension installed, then replace the O2.



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Discussion Starter #3
I just got it last night so the only maintenance I have was the seller's reports which was 3k oil changes, spark plugs and wires 2 years ago, tranny service 2 years ago, and brakes. Fluids look good now, but I plan a full fluid change here soon.

What kind of diagnostic would I ask for?
 

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see what the fuel air ratio, trims and such are all doing. This will show the issue if there is one.
Tigris mentioned the checks ^^^.

But as he said, do the maintenance first. At 100K miles, recommended maintenance is new Iridium plugs, valve adjustments, filters, etc. (Interesting note about spark plug wires since it doesn't have any...) :rolleyes:
 

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Discussion Starter #5
So far I've done my oil, tranny fluid, and air filter. typical new owner stuff. No code yet. It's been roughly 500 miles
 

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Discussion Starter #7
Ok so this thing just puts the sensor further away from the converter, causing it to not read the bad combustion?
For reference it has 161k
 

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it helps it store oxygen like a good converter does,if you look at the live data on the downstream O2 and hold the RPM at 2k on a good and hot converter and no exhaust leaks the numbers shouldn't go up and down like the upstream even at idle it should be slow response compared to the upstream ,that's the converter storing oxygen to convert the bad HC and CO to CO2 and H20 when it needs more O2 to burn off or light off,I had to edit so its just fooling the sensor not making the converter work better just to be clear
 

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Discussion Starter #9
well crap i spoke too soon. It literally came on today. So it'll just bridge the threading from the sensor to the sitting on the converter then? I don't have the interest of making this thing run perfect, so I'm fine with a quick fix.
 
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