Why is my car still pulling P0420 code

Question

Why am I still getting a P0420 code after replacing both catalytic converters and all 4 o2 sensors on my 2002 Toyota Sequoia limited.

Answer 1

P0420 Catalytic below threshold Bank 1

You are going to have get the data stream of what the engine management is doing. This will help in determining the cause of why the catalytic has failed or if the catalytic convertor has failed. Listed here are some example of what you will need

Here a false code of P0420 here the downstream 02 which monitor the catalytic convertor has internally  failed, the fix here was to replace the downstream 02 sensor for P0420

​ Here another P0420 , in this case a good catalytic convertor the rear 02 sensor should stay above .650 volts, Holding the RPM at 1500 RPM the rear 02 reports a good catalytic convertor , allow to idle the 02 sensor voltage sensor would drop and go back to .650 volts within 20 seconds, but in this case it stayed below .650 volts until higher RPM . In this case the catalytic has failed