2007~2015 Catalytic Converter/O2 Sensor Issues

Hi All-

Having some trouble with P0420 and P0430 codes (2012 CX9, 140k miles). This past summer car had P0420, took it to local mechanic who replaced the Bank 1 Upstream O2 sensor...did not solve the problem. I then bought a new set of cats and brought them to him, he replaced Bank 1 Cat and the downstream O2 sensor, then handed me back the Bank 2 cat and said hold off on replacing that one. This did not work, CEL still on, so I waited until this past week when I had access to a lift and I replaced the Bank 2 Cat and both O2 sensors (estimate I drove 8k miles in between replacing Bank 1 Cat an Bank 2 Cat). But the CEL is still coming on after driving for approx 20-30 miles...both P0420 and P0430.

So now both cats are new as are all 4 O2 Sensors. Plugs, Coil Packs, and all fuel injectors were replaced at 100k. No noticeable exhaust leaks, and no driveabilty issues...car idles perfectly, and runs very well.

Is there some type of drive cycle sequence to be performed after completing all of the above work in order to clear the codes? Or am I missing something else that can be triggering these codes?

Thanks!

Brian
 
:
2010 CX-9 GT
Did the insides of the catalytic converters look ok? Not melted, broken, or otherwise damaged?

Did you reset the ECU by disconnecting the battery?

If none of that leads anywhere, the next thing to look at is the long term fuel trims in the ECU. You might have a bad or dirty MAF or a vacuum leak, which is causing the engine to run so lean or rich that the O2 sensors can't see a change in the makeup of the exhaust gas going into and leaving the cats.
 
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Did the insides of the catalytic converters look ok? Not melted, broken, or otherwise damaged?

Did you reset the ECU by disconnecting the battery?

If none of that leads anywhere, the next thing to look at is the long term fuel trims in the ECU. You might have a bad or dirty MAF or a vacuum leak, which is causing the engine to run so lean or rich that the O2 sensors can't see a change in the makeup of the exhaust gas going into and leaving the cats.
Ty I will disconnect the battery and see what happens. I think my scanner can measure fuel trims (Launch CRP123). The cats are brand new and looked good, one was put on by a local mechanic about 5/6 months ago, the other I just pout on myself this week, and it looks pretty good, no visible damage.
 
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:
Northeast
:
2020 CX-5 Tour
Ty, I'm not the best with checking electrical gremlins, so I may need to seek help for that...unless it is plugging in a voltage meter and reading, that I can do.
Aside from a visual examination of the all the O2 sensor wiring you can see, the complete job consists of doing a resistance test of all of the circuits. And that requires a diagram of the O2 sensor wiring, and using it to check continuity from the O2 connector pins to their respective pins on the ECU connectors. Not a difficult job at all, once you have the correct wiring diagram.
 
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Aside from a visual examination of the all the O2 sensor wiring you can see, the complete job consists of doing a resistance test of all of the circuits. And that requires a diagram of the O2 sensor wiring, and using it to check continuity from the O2 connector pins to their respective pins on the ECU connectors. Not a difficult job at all, once you have the correct wiring diagram.

Ok ty that I can do
 
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Wanted to provide everyone with an update. It looks like the culprit is the inexpensive ebay aftermarket catalytic converters I used for the replacements...Mazda dealership says the O2 sensors are working but the car is basically rejecting the cats as they are pretty far out of spec from OEM. Lesson learned in trying to save $...should have bought the OEM cats to begin with. Once I get the OEM cats on I will report back if it solved the CEL issue.
 
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