O2 Sensor Voltage to AFR Conversion and P0420

[afmcgraw]

Just got my first P0420 catalyst efficiency code. Mine's a 2000 with about 206K, and AFAIK, my cats and sensors are original. Before I go and replace the cat(s)...or do nothing, I want to make sure that it's not something else.

Does anyone have the voltage to AFR characterization of the wideband and narrowband O2 sensors? I took a log on my commute home, and my ranges are the following:

B1S1 spends most of its time at 0.5V (cruising) or 0.37V (lean burn)
B1S2 is all over the place at cruising, or 0V (lean burn)

So it appears that they trend together at lean burn, but it would be nice to be able to convert it to AFR. I realize that the narrowband can have a large range of outputs for 14.7:1, but it seems like it should be a bit steadier under consistent conditions and B1S1 output.

Also, does anyone have any OSC index data for the Insight? Mine was 3584 when I got the CEL with a listed min of 3606. Now that I reset the code and went through a drive cycle, my OSC index is 4728 with a listed min value of 3879.

Here's the data for fun:

[Eli]

Instead of posting a screencap JPEG, Save the graph As a PDF.

Hmm. I found this:



We use a NTK L2H2. Searching....

That formula is widely cited. Either 2 * Voltage + 10 or 2 * Voltage + 9.

[Eli]

Hmm.. I think maybe our primary O2 sensor isn't the linear type... Still researching as I can at work...

This may be for the L2H2:

http://wbo2.com/2a0/afrnbb.gif