Circuit Description
WARNING: This page is about a different car, the 2003 Lexus LX 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, after engine and catalyst are warmed up, and while vehicle is driven within set vehicle and engine speed range, waveform of heated oxygen sensors have same amplitude. See Fig 1. Possible causes are:
- Exhaust system leaking.
- Defective heated oxygen sensor.
- Defective catalytic converter.