Circuit Description
WARNING: This page is about a different car, the 2003 Lexus GX 470. However, it is still accessible from the selected car via links, so may be relevant.
ECM compares waveform of heated oxygen sensor No. 1 (located before catalytic converter) with waveform of heated oxygen sensor No. 2 (located after catalytic converter) to determine if catalytic converter performance has deteriorated. If both waveforms change at similar rate, catalytic converter performance has deteriorated. DTCs are set when all heated oxygen sensor bank 1, sensors 1 and 2 waveforms have same amplitude after engine and catalyst are warmed up, and vehicle is driven for 5 minutes at 20-50 MPH (2 trip detection logic). For normal waveform see Fig 1. Possible causes are:
- Exhaust system leaking.
- Defective heated oxygen sensor.
- Defective catalytic converter.