Which catalytic converter gives P020 code

Good evening.

The 420 is set when the rear O2 sensor reading is not steady. If you look at the reading, you need to see around 4.5 volts and it may vary by only .1 or .2 volts either way. When it varies more than that, the sensor starts to act like the front sensor.

The only job of the rear O2 is to monitor the catalytic converter. When the readings are off and the code sets, then the cat is worn out and needs to be replaced. The precious metals inside are no longer doing there job processing the gases from the engine.

Roy

Thanks Roy. From all my Googling I saw how the downstream O2 sensor should work (wish I had the tool that showed those nice wave forms). My confusion is about which catalytic converter is bad, and correspondingly, which cat has the O2 sensors above and below it? Your diagram seems to indicate it is the vertical catalytic converter right off the exhaust manifold in the font of the engine - which is also where the upstream Air Fuel Ratio Sensor is (under the heat shield), correct? But I have read elsewhere it is the horizontal cat further down the exhaust line under the body. Thanks.

On the Camary, it is the one that is part of the exhaust manifold.

420 is bank 1 catalytic converter you only have 1 bank.

https://www.rockauto.com/en/catalog/toyota,2002,camry,2.4l+l4,1434102,exhaust+&+emission,catalytic+converter,5808