Circuit Description

ECM compares waveform of Air/Fuel (A/F) sensor (located before catalytic converter) with waveform of heated oxygen sensor No. 2 (located after 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 warmed up. Possible causes are:

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