I ve also Rav4 other than prius and it threw the code po420. I think due to first o2 sensor not working. I assume the first graph supposed to be up-downs after quick research. Am I right? Posted via the PriusChat mobile app.
That code is for the catalyst being below the threshold of performance according to its internal test that it runs every so often If the O2 sensor downstream was bad I think there is a separate code for that so there's always that we may be able to check the O2 sensor with just a regular DVOM ohm meter etc. once the catalyst can't pass the test that the car runs this is the code you get I do believe there are codes for the O2 sensor upstream and downstream that are different
