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Background: 2006 2.4L RAV4, 229,000 miles. I have searched through the forums on this site and had multiple hits on the CEL code P0420 but not (yet) found the help I need. Plus I dealt with the issue of a failed cat less than 2 years ago. I'm using an ELM327 wifi OBD-II reader coupled with DashCommand to attempt to diagnose the current issue. I've included 3 screen shots from DashCommand showing what I hope is relevant data (ignore the 3 "Quick Gauges" on one of the screen shots. The focus of that screen shot is the O2 sensor voltages.) These screenshots were taken after approx. 20 minutes of driving at as close to steady state 55 MPH as possible.

The newest occurrence of the P0420 happened a week ago. There were no additional codes. I reset the CEL, and after 2 or so drive cycles it reappeared. There are no new/noticeable driving issues with the vehicle (rough running, misfire, stalling, etc). This vehicle does consume approx 1 qt oil per 1,000 miles. I've had the oil consumption test done but it "passed".

Relatively recent maintenance that has been done that may be relevant:

  • New spark plugs at 204K miles
  • New ECM at 208K miles
  • New cat at 208K miles
  • Cleaned/inspected MAF sensor at 229K miles
  • Cleaned/inspected PCV valve at 229K miles
Given the low mileage on the cat I am wondering about a failed AFR (upstream O2) sensor or O2 (downstream) sensor. Note that DashCommand shows no data for the O2 sensor. For those familiar with DashCommand, I have done an aggressive PID detection.

I would appreciate any help in next steps diagnostics.

Thanks!
 

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Typically you see a PO420 after you replace the upstream O2 sensor without replacing the aft one. Since you just replaced the cats, it would seem like they would be in good shape. Have you ever replaced the O2's. Might be worth a shot.
 

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MrPulldown - thanks for the suggestion. I am getting close to pulling that trigger but have continued to do a bit more debugging before potentially spending money on unnecessary parts.

After watching a video by EricTheCarGuy on YouTube (
) I checked the temp of my cat at intake and exhaust. About 100-150 hotter at exhaust implying, at least per the video, that the cat is generally in good working order (which is what I expect). I next examined the exhaust system to the best of my ability (I forgot to grab my mirror on a stick to look at the top of the pipes) and didn't see any obvious leaks. I then plugged the exhaust with a rag and listened for leaks - again nothing obvious. My next step is to look at the top of the pipes and then (assuming all looks good) tighten all of the joints in the exhaust system. If that fails to correct the problem I will next try replacing the O2 (secondary) sensor.

Doing the above (specifically checking the cat temp) was educational if only because the cat was not where I expected it to be. I expected it to be under the vehicle, somewhat in-line with the muffler. Nope - way up front, hanging vertically from the manifold.

One thing I forgot to mention in my original post, I did try running a bottle of CataClean through the system with no change in error code.

Again, suggestions welcomed.
 

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Today I replaced the O2 sensor (Denso OEM). No change. Next step is to try the sensor spacer/anti-fouler. I know that's not a "real fix".
 
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