Circuit Description
ECM observes waveform of heated oxygen sensor, located behind catalyst, to determine whether catalyst performance has deteriorated. If catalyst is functioning normally, waveform of heated oxygen sensor switches back and forth between rich and lean much more slowly. When waveform of heated oxygen sensor alternates flatteringly between rich and lean, it indicates that catalyst performance has deteriorated (2 trip detection logic). See Fig 1. Possible causes are:
- Leak in exhaust system.
- Faulty A/F sensor.
- Faulty heated oxygen sensor.
- Faulty catalytic converter.