Circuit Description

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. When both waveforms change at a similar rate it indicates that catalyst performance has deteriorated.

DTCs are set if after driving vehicle for specified period of time with engine at normal operating temperature, oxygen sensor waveforms are the same (2 trip detection logic). Possible causes are:

• Exhaust gas leak.
• Faulty catalytic converter.
• Faulty heated oxygen sensor.