Hi all,

I have a question about post catalytic converter O2 sensor voltage. When car is at operating temperature (191 F) the voltage is near 0.2 V @ idle, and 0.65-0.74 V @ 2000 RPM. Are those voltages normal, or is it too rich @ 2000 RPM?
I previously had the CEL on code P0420, replaced the cat converter and CEL went off after 20 something miles.

Thanks!

And it'* for an 04 Buick LeSabre!

Here is a graph of a pre and post O2 sensors.....

The first is the pre.......notice the O2 reading is constantly crossing the midpoint of .45 volts, and is not staying high or low......this is what a good pre should look like......

The second is a good post O2 sensor.......notice how there are no rapid changes....the voltage will be high or low depending on how the catalyst is using the oxygen in the exhaust......

The third is graph is a result of a bad cat......notice the rapid changes and how it kind of "mirrors" the changes in the pre O2 sensor.....

So when you have a good cat, that post O2 sensor will change slowly, staying high for awhile, but mostly low, and will not mirror the pre O2 sensor....

Nice post T2.

Thanks Tech II!! That'* what my new cat is doing.