O2 Sensor - normal readings? 2014 CX-5


Current '14 CX-5 GT, previous Miata 2xNA, NC & Mazda 5
My 2014 CX-5 GT developed some problems when I went overboard with carb cleaner and Berryman's Chemtool when I was cleaning the intake.
I now have a P0421:00-27 Efficiency Of Catalyst 1 Is Lower Than Limit - Bank 1 DTC.
I've tried used up a gallon of lacquer thinner originally, which cleared out the check engine light, but now it's back.

Using my X-tools D-7, I can see that the bank 1, sensor 1 reading is fluctuating wildly, from -632 to + 482, when the reference range (as provied by Xtool) is -2 to +2.
Since I haven't the experience with seeing the normal range, can anyone tell me if my O2 sensor is shot or something else might be wrong?

The other sensor, bank 1 sensor 2 (I presume after the cat) appears steady.
So I replaced the upstream AF sensor (NTK 27008) , and I still had the code. Looking back at the data logs over time, before and after I did my intake cleaning (which started me on this mess). I noticed the rear O2 sensor would never read below 0.50. This sounds like the sensor is bad. Going to replace the rear sensor and see what happens.
Curious if you ever fixed this issue? I'm also getting a P0421 for quite some time now. It runs fine but had to do plugs twice in the last 2 years. I use the Torque obd app and wondering what you are getting for voltage values on both "Sensor 1" and "Sensor 2"? I get sensor 1: Wide Range Current, and wide range equivalence, but NO voltage. Sensor 2, I only get voltage. Just wondering if it's the app or if it's the O2 sensors. I don't have problem replacing the CAT, but don't want to just throw parts at it.
I replaced the rear sensor with a Bosch. CEL went off, but came back. My scan tool did pick up a wider range from the new sensor, but it reacted too quickly to changes in throttle, compared to the front AFR. I bought a $11 laser thermometer and measured the temps going in and out of the cat. 88 degrees in, 298 degrees out, ambient temp 40F. Cat is good. Just ordered a NTK rear O2 from rock auto. hope this finally works.
.... I bought a $11 laser thermometer and measured the temps going in and out of the cat. 88 degrees in, 298 degrees out, ambient temp 40F. Cat is good. ...
88 degrees means you would have been ok grabbing that exhaust system pipe with your bare hand. And everyone knows what happens if you do that, even after just a few minutes running. So, either you must have measured those temps immediately after a stone-cold startup, measured incorrectly, or the tool is no good.

Aside from that, the fully warmed-up operating temp of the cat itself is what matters, and a normal warmed-up range is anywhere from 750F to 1500F, depending on vehicle. Also, the temp of the cat alone doesn't indicate if a cat is good or bad, because what really matters is the quality and condition of the catalyst, and also that the flow through the cat is adequate (i.e. not plugged).

IMO, the catalyst of your vehicle's cat was damaged by the chemicals you used to do the cleaning, and you'll need to replace it if you want to get rid of that code, sorry to say.
I agree with what @edmaz said. Regarding O2 sensor readings, the computer ignores them until the O2 sensor is hot enough to provide valid numbers, usually above 650*F. At that point the system is referred to as being in "closed loop" meaning the O2 sensor is now included since it's hot enough to function correctly and provide valid signals . On cold starts the system is referred to as being in "open loop" until the O2 sensor comes on line.
The chemicals could have 'poisoned' the O2 sensors and cat. I'm not sure if a long high speed trip on the interstate would clean up the cat or not. I have no experience in that area. Good luck.
Final note. I like to put Japanese sensors and plugs in Japanese cars (like Denso, NGK etc.) German cars get German stuff. Done so as to match what came with the car if possible.
Thanks for the input, but there are too many variables. My only concern, is whether or not the catalytic converter is doing its job or not. If the temperature exiting the converter is hotter than what goes in, then it's working. In my case, it's a 200 degree rise. And yes the car was driven for over an hour (so it's in closed loop), but because of the cold weather, engine at idle (not at 2500 RPM as some mechanics suggest) and where I took my measurements (on the incoming pipe, and exiting pipe, not on the heat shield, or a hole through the heat shield, I am not going to hastily conclude that my catalytic converter is failing.

Video demonstration of how to use a laser thermometer to test a catalytic converter.

It is simply incorrect to think that if a cheap laser thermometer did not read 750F to 1500F degrees, that the catalytic converter is bad. Internally, it may reach those temperatures, but if you have a 1500F degree source of heat under your floorpan, you have more problems such as unburnt fuel reaching the converter and burning it from the inside out. What is important, and I will repeat again, is if the temperature exiting the converter is higher than the temperature before the converter.
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Screenshots from my Xtools D7 (not cheap)

Bank 1 Sensor 2 - narrow band but the range is much wider (from 0.35 to .94v). The sensor that it replaced only showed 0.50 to 0.65v


The old AFR sensor showed had a range between -632 and +482. This one has a much wider range!
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Final note. I like to put Japanese sensors and plugs in Japanese cars (like Denso, NGK etc.) German cars get German stuff. Done so as to match what came with the car if possible.

I can agree with that. The NTK sensor was installed a few hours ago, appears to be working much better. The previous posts shows the range of values ( 0 - 1v ) which is considerably more than what Bosch put out. I use NGK plugs and coils.

Sensor 1 air fuel ratio sensor is what the ECU uses to change the air/fuel mixture entering the combustion chambers. This is important for performance and fuel economy.

Sensor 2 only measures the output from the catalytic converter. It is not used to control anything on the engine. Why? because Sensor 1 is closer to the engine and the inputs are not contaminated by other systems (e.g. a cat).

Sensor 2 doesn't have any significance other flashing than the check engine light. Older cars don't have a sensor after the cat. It's only mandated by stricter Federal emission laws of late.

Yes, I cheaped out by buying Bosch because I didn't think it was important. But that orange CEL was driving me crazy. Rock Auto sold both Bosch and NTK - you would think they only sold things that work. Lesson learned.
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