OBD2 oxygen sensor signals

[flyingscot]

On my 2-channel oscilloscope, what should the secondary (after cat) O2 sensor output look like - compared to the primary (mixture control) O2 sensor? - for both closed-loop and open-loop modes. Should the secondary sensor output be a higher voltage level - on average?

[AcuraTech]

The post-cat O2 sensor should have about the same average reading as the primery sener, however the second sensor should be a lot more stable, staying closer to .45volts, with slower shallow cures