Interpreting O2 Sensors

[CapeX5]

Attached is a short video of my O2 sensors before and after CAT. 03 4.6IS 190K miles. Getting a code on my FOXWELL. Thoughts on the after O2 not changing? I am just trying to figure out whether my "cat efficiency" code is the actual CAT being bad or just the sensor.
https://www.youtube.com/shorts/ZXR_liokyWk

[X5chemist]

The video is set to private.

What are the high and low readings? If it’s not changing, the sensor is likely toast. Especially if it’s an original with so many miles. Can it read cat temp?

[CapeX5]

Originally Posted by X5chemist

The video is set to private.

What are the high and low readings? If it’s not changing, the sensor is likely toast. Especially if it’s an original with so many miles. Can it read cat temp?

X5, thanks for letting me know about the video. I "think" I fixed it. The pre cat is going between 0-1volt. The post is steady at .47. Hopefully you can see it. I realize that sometimes codes are erroneous and the actual problem lies elsewhere.

[X5chemist]

If a cat is going bad or bad, P0420 or P0430 codes are present. Assuming O2 rear sensors are working properly.
Rear V reading should be around 0.45. The code may have been set because the rear sensor took too long to warm up. I would reset it and drive it. See how long it takes to come back if it does.

[workingonit]

Originally Posted by X5chemist

... Assuming O2 rear sensors are working properly.
Rear V reading should be around 0.45....

From a Google search:
O2 voltage range, per NGK

I copied a graph made using the Torque Pro android app onto my PC for posterity, while hunting (both false, it turns out) P0171 & P0174 codes.


The bank 1 sensor 2 (after-cat) dips as low as .2v, and bank 1 sensor 1 (pre-cat) goes as high as .9v. Please note that both of the after-cat sensors (b1s2 & b2s2) didn't warm up for about 1.5 minutes, according to my graph. Make sure you're seeing similar warm-up times for your after-cat sensors...mine were relatively new (about 2.5 years old, according to the previous owner) when I made this graph.

[X5chemist]

Front O2 sensor are monitored for air/fuel injection. Rear O2 sensors monitor catalyst operation. When rear O2 sensors mirror front ones, the cats are probably toast.