O2 sensors

[Webpirate]

Hello
I have a 2006 volvo s40 2.4i with no check engine lights. I was just adding graphs to my torque app screen when I noticed that my pre cat O2 sensor was stable and my post cat O2 sensor was fluctuating..

Is that normal for the volvos? Is the front sensor an Afr sensor instead of a regular O2 sensor??

[Webpirate]

Better readout different app