first lambda needs to be waving from around .2 to .8 volts at idle - anything more than .8 means it is running rich and it needs to drop below .4 volts otherwise it is considered rich
the 2nd lambda needs to be more consistent around .3- .6 volts and should not be anywhere as wavy as first lambda , you should notice it might increase in voltage when at a higher ref to account for more emissions passing through the cat but should not be irratic in any way
if it is is showing the same sort of voltage increase & decrease as the first lambda than ya cat aint doing its job, also the first lambda should be fluxuating every second or so otherwise it is fault
note the readings show this at idle when engine is warm
A good O2 sensor should produce an oscillating waveform at idle that makes voltage transitions from near minimum (0.1 v) to near maximum (0.9v). Making the fuel mixture artificially rich by feeding propane into the intake manifold should cause the sensor to respond almost immediately (within 100 milliseconds) and go to maximum (0.9v) output. Creating a lean mixture by opening a vacuum line should cause the sensor's output to drop to its minimum (0.1v) value. If the sensor doesn't flip-flop back and forth quickly enough, it may indicate a need for replacement.
If the O2 sensor circuit opens, shorts or goes out of range, it may set a fault code and illuminate the Check Engine or Malfunction Indicator Lamp. If additional diagnosis reveals the sensor is defective, replacement is required. But many O2 sensors that are badly degraded continue to work well enough not to set a fault code-but not well enough to prevent an increase in emissions and fuel consumption. The absence of a fault code or warning lamp, therefore, does not mean the O2 sensor is functioning properly.