Hello, so I have a 2007 Prius with 146K on it and I started getting the P0420 code. I scanned it and it shows "Catalyst System Efficiency Bellow Threshold (Bank 1)" I have been resetting the code and after about 300 miles it keeps coming on again. Is it safe to say that my Air/Fuel Ratio/O2 sensor is bad? Also if anyone has the OEM part number for both the upstream and downstream sensors that would be appreciated.
It would be safer to say that the catalytic converter is getting marginal. If you replace the A/F ratio sensor that might help and might not. Regarding parts numbering, you might consult one of the Toyota dealer websites with parts catalogs. For example: Toyota Parts - Genuine Accessories | AutoNation Toyota Gulf Freeway Parts
Recent thread here some folks are using this stuff How to Use Catalytic Converter Cleaner and Which Product to Buy
