Circuit Description
WARNING: This page is about a different car, the 2003 Lexus GS 430. However, it is still accessible from the selected car via links, so may be relevant.
The ECM compares waveform of oxygen sensor located in front of catalytic converter with waveform of oxygen sensor located behind catalytic converter to determine if catalytic converter performance has deteriorated. If catalytic converter is functioning properly, waveform of oxygen sensor after catalytic converter will switch back and forth between rich and lean much more slowly than waveform of oxygen sensor in front of catalytic converter.
DTCs are set if after driving vehicle for specified period of time and speed and engine is at normal operating temperature, oxygen sensor waveforms are the same. See Fig 1. DTC P0420 is for bank 1. DTC P0430 is for bank 2. Possible causes are:
- Exhaust gas leak.
- Faulty oxygen sensor.
- Faulty catalytic converter.