Odd OBD2 readings with possibly false P0420...


masanders

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I’m getting some odd readings on my OBD2 scanner that don’t make sense. I’m hoping someone can help me out. The readings I’m referencing come from my wife’s 2007 Escape with the 3.0L V6 engine. I’m getting a P0420 with no real symptoms of bad cats like rough driving/operation or loss of power. The O2 sensors are reading as if the cats are bad though.
45953


The Commanded Equivalency Ratio should be roughly .95. The reading I’m getting is 126.002.
45954
Something is wacky in the system. I replaced a broken vacuum line and the pcv valve tonight which seemingly improved acceleration, but I might be seeing change where there isn’t any.
Tomorrow I’m going to fully disconnect the battery, clear the KAM, remove and inspect O2 sensors, check O2 wiring for damage, and whatever else I can think of.

I honestly think this is a false P0420, but I’m in need of ideas and suggestions.
 


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Dirtman

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The secondary 02 sensors are switching in sync with the primary sensors. The only way this happens is if the exhaust gas is the same between the primary and secondary sensor. I.E. cat isn't burning anything up inbetween. If the cat is burning up the exhaust gasses as it should the secondary o2 sensors should run at a steady voltage. The readings there show this happening on both banks, I'm not sure how the exhaust is setup but it would be an anomaly to have two cats go bad at the exact same time.
 

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Cats can go bad without failing mechanically. The catalytic converter performs a chemical reaction and they can be not working chemically without the beds breaking down physically, so bad cats does not always mean plugged cats.
 

masanders

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Replaced the two downstream O2 sensors and cleared the memory which resulted in no change in the waveforms.
These cats are only 3yo.

The cats aren’t plugged, but I still don’t understand how they could have failed.
 

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Temp test them, go for a drive so the car is nice and warmed up and take a reading. If the temperature at the inlet of the cat is the same as the outlet then the cats are not functioning. I can't tell you why, but that would confirm the cats are dead.
 

8thTon

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I've had P0420 due to bad plugs causing misfire on my old Cougar's 2.5 Duratec V6. Keep in mind that O2 sensors only sense oxygen - if the mixture fails to fire then unburned fuel and lots of extra oxygen come out. It was not a real obvious misfire, usually under heavy load at low rpm, but after a while it would set the code.
 

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I don't think I've ever seen a P0420 caused by anything but a cat failure. What brand are your 3 year old cats?
 

masanders

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I don't think I've ever seen a P0420 caused by anything but a cat failure. What brand are your 3 year old cats?
I don’t remember the brand. I know they weren’t a major name brand though.
 


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