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P0420 Code 2005 CRV

11K views 18 replies 4 participants last post by  bradleydavidgood777 
If the O2 sensors are original at 230K miles, then it's probably time to replace them. Just might fix the P0420. Replacing the rear O2 sensor on a different car I had resolved the problem. Also, check the function and flow of the cat by using an infrared laser thermometer and check the temp of the exhaust pipe right before and right after the cat. After cat temp should be much higher than before cat temp. If the after cat temp is nearly the same, then the cat is probably plugged up and/or non-functional. If you car is running rich or burning oil, that will either kill the cat or cause it to not function until it's cleaned.
 
Missing some details of that test just fyi. Firing up a cold engine and trying that wont yield anything useful. Engine needs to be at operating temperature

Not trying to be a jerk but giving bad info is kind of pointless and not helpful. Quit using google and leave it to the techs. Live data and freeze frame, forget what's the emoji for "facepalm".
Yes, I am aware that it must be a fully warmed up engine and I did mention that in another thread with a similar issue and just neglected to mention that here. I also did not suggest to Brad that the engine should be cold. My suggestion is not "bad info" even if it's incomplete because I forgot to mention something. I post lots of threads and can't perfectly mention every detail each and every time. If Brad would have responded, I would probably have mentioned to him that the vehicle must be fully warmed up.

You're "not trying to be a jerk"? OK, I believe you, but you are coming across that way, just so you know. There is a proper and helpful way to say things, then there is an arrogant way to say things. You're a tech? Cool, then act like a professional with the heart of a teacher instead of trying to draw flies with vinegar because you're so flippin' awesome and we are all just a bunch of idiots. This forum is for everyone, not just techs. We are here to help each other and bounce ideas off each other and share our experiences and whatever knowledge we have. I have repaired an issue similar to this, so suggested the thermometer test. I have helped MANY people on another forum and am well known there to be helpful and to save people money and not insult those with less skill than I have. I have very patiently and kindly guided those with less knowledge than I have. Why? Because I care about my fellow human beings and want to help them. Are you here just to be right and smart and show us how awesome you are?

Maybe you are a skilled technician, and perhaps the greatest diagnostician on the web, but you have something to learn in how to get on with other people.
 
It should be much hotter after the cat if it is working properly. That's how I knew mine was messed up, because it was about the same. Here's a video:

 
Thanks, I watched the video. I still am wondering how much hotter it should be, about. Thanks
Umm......like 75 or 100 degrees hotter or even more. Something like that. So, if the incoming is at say...….350 degrees, then the outgoing exhaust might be 425 or 450. I wouldn't get caught up on an exact number, but just that it is much hotter coming out of the cat than it is going into the cat. I can't explain the physics of it, but the catalyst material, if working correctly, actually increases the temp of the exhaust. If the temp isn't increased, then it's not working.

You'll want the vehicle fully warmed up (maybe some highway driving would help). When I did the temp test (on a Mazda Tribute) I increased the RPMs a bit to increase flow. In my case, the temp at the rear of the cat was about the same as the front of the cat (it might even have been a bit lower? I can't remember). That's when I knew something was wrong with the cat. I removed it and found it was all plugged up. A cat can also be non-functional even if it is very clean on the inside. After 350K miles on my Toyota Corolla the cat just isn't working even though it's clean. It was burning extra fuel earlier in it's life due to lean conditions (intake) and I think that helped kill the cat. I put a spacer on the newer rear O2 sensor and the car still runs fine now 40K miles later, which is 390K miles.
 
So, hook up a scanner and see what kind of readings you're getting from both the O2 sensors. I'm sure there are lots of videos on YT about how to interpret the readings. In my case with a Toyota, replacing the rear O2 sensor fixed the P0420 for about two years.
 
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