Hello friends,

I have a 2002 Sebring 2.7L that is throwing P0420. The description of the code points to needing to replace the cat but I'm trying to be thorough in my troubleshooting. I collected voltage data on the Bank 1 O2 sensors as show in the attached graph.

My question is about the middle part of the graph when the vehicle was being driven at about 45 MPH for 60 seconds or so. The voltage of the O2 sensor after the cat (orange line) doesn't drop below 0.7 volts for most of the duration. Would this be the expected behavior if the cat is in fact faulty or does this indicate an issue with the sensor itself?

My feeling from this graph is that the cat is in fact not working properly since the second sensor is constantly reading rich.

Any thoughts?

Thanks for your time!

-James