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I don’t think the cause of the failure will make any difference in diagnosis. I don’t believe it really matters HOW it fails, you could still use these methods to diagnose a bad converter. That said, you should address the root cause or your new converter will suffer the same fate as your old one. It is true that you need to address any engine performance issues before you replace a converter. If not, it will be a very expensive lesson.
Thanks for your input.
Hi Eric, in regards to your video about diagnosing a P0420 code, I have the same problem and used a OBD2 scanner to read data from the O2 sensors.
On bank 1, and revving around 2k RPM, the pre-cat O2 sensor was moving from low to high values back and forth like you said it should be doing, but as far as the post-cat sensor, it was staying around .9V which is quite different from what you had on your scanner for a bad cat. What would this mean in my case?
Thank you for your time
[quote=”Wiglud” post=94483]Hi Eric, in regards to your video about diagnosing a P0420 code, I have the same problem and used a OBD2 scanner to read data from the O2 sensors.
On bank 1, and revving around 2k RPM, the pre-cat O2 sensor was moving from low to high values back and forth like you said it should be doing, but as far as the post-cat sensor, it was staying around .9V which is quite different from what you had on your scanner for a bad cat. What would this mean in my case?
Thank you for your time[/quote]
It might mean a bad O2. You might also want to check the temps as shown in the video to verify the catalytic converter operation. If it’s operational, then that could verify an O2 sensor problem. Mostly with a P0420 it’s the catalytic converter and not the O2 sensor that’s at fault.
Any idea how the O2 sensor data would look with a pre-cat exhaust leak?
My 2004 Subaru legacy has a manifold mismatch due to an engine swap. It’s the California emissions version, so I have three cats and 5 O2 sensors (2 are A/F). I can read OBDII with RomRaider and/or Torque.
I bought a junkyard header and I’m headed to a muffler shop this week, but I’m hoping it’s not actually the cats. Thanks!
[quote=”Joeboo25″ post=114169]Any idea how the O2 sensor data would look with a pre-cat exhaust leak?
My 2004 Subaru legacy has a manifold mismatch due to an engine swap. It’s the California emissions version, so I have three cats and 5 O2 sensors (2 are A/F). I can read OBDII with RomRaider and/or Torque.
I bought a junkyard header and I’m headed to a muffler shop this week, but I’m hoping it’s not actually the cats. Thanks![/quote]
You can always check the temperature of the cats to see if they function like in the video. That’s the way we did it before OBDII.
Yeah, I think that’s the next step and I already have an IR thermometer. I’m hoping the manifold swap will normalize my sensor data. But even if it does, I’m still taking the temperature because it’s such a neat test.
Wait till you see the new toy I got today in action. It will be a bit before I do the review, but when I do, I’ll be headed strait for some cats to try it out on.
Eric thanks for all the awesome videos. I see all these videos and information online diagnosing a catalytic converter / oxygen sensor failure on 4 cylinder videos. It seems fairly simple with less variables.
My issue is a 2007 Honda Accord Hybrid (V6) with the P0430 and P0420 codes only. It is commonly assumed by the diagnoser that the catalytic converter has failed when they see the P0420. In my case, if you apply that logic it would imply both converters have failed! I believe the issue is actually a “lazy” oxygen sensor.
However it is extremely tough to reach that diagnosis when you add to the mix 2 A/F sensors and 2 oxygen sensors measuring data. Can you do a video on a topic like “lazy” oxygen sensors and “oxygen sensors mirroring”?
Can you do a video related to this item?
Eric,
Thanks for posting this video. I’m having a problem on my 2005 Subaru Legacy. I’m getting the P0420 code which caused a CEL to come on and disabled my cruise control. :pinch: After watching your video, I made a trip to autozone to barrow there code reader so that I could measure the O2 sensor voltage. I also used an IR thermometer on the input and output of the cat. The temperature test showed about 400deg on the input and about 500deg on the output (suggests cat is working). But I noticed something very odd on the O2 voltage readings. The down stream sensor moved in range a between 0.2 to 0.8 volts. I assume this is why the code got set. But the upstream voltage read a constant 2.75V. Does this mean the upstream O2 sensor is bad?
The only other code that got set was on saying something about a loose gas cap.
Any help appreciated.
Thanks!
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