P0420 Fault Code on 2000 Camry V6 LXE - Possible Bad Converter or Rear O2 Sensor?
About three weeks ago, I had the exhaust pipe with catalytic converter replaced on my 2000 Toyota Camry V6 LXE. The original pipe was severely rusted at one of the mesh elbows. Approximately a week after installation, the vehicle triggered a P0420 diagnostic trouble code. I've ruled out the new catalytic converter as the cause since it's a brand-new unit. Last year, I replaced both front oxygen sensors, and I believe that issue is also unlikely to be responsible (though not completely eliminated). The remaining possibilities are either a faulty rear oxygen sensor (located after the converter) or an exhaust leak. I inspected the entire exhaust system under the vehicle and found no visible leaks. Based on forum discussions, could it be possible that my newly installed catalytic converter is defective? I returned to the muffler shop for further inspection, and they suggested a faulty rear oxygen sensor—most likely the one after the converter—as the root cause. However, replacing an O2 sensor costs around $100 per unit, and I'm hesitant to proceed without being certain of the diagnosis. Are there any other diagnostic steps or considerations that could help identify the actual issue?
As there are no other diagnostic codes, you're correct—either a sensor issue or the catalytic converter is at fault. A scan tool is needed to read the rear O2 sensor data and see what the Powertrain Control Module (PCM) is actually detecting. Key factors to consider: - The quality of the catalytic converter installed - Any modifications or aftermarket parts in the exhaust system