Circuit Description

ECM compares waveform of Air/Fuel (A/F) sensor (located in front of catalytic converter) with waveform of heated oxygen sensor No. 2 (located behind catalytic converter) to determine if converter performance has deteriorated. If both waveforms change at similar rate, catalyst performance has deteriorated. DTC is set when A/F sensor and heated oxygen sensor No. 2 waveforms have same amplitude after vehicle is driven for 5 minutes at 20-50 MPH. Possible causes are:

• Exhaust system leak.
• Defective A/F sensor.
• Defective heated oxygen sensor No. 2.
• Defective catalytic converter.