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 driven for 5 minutes at 20-50 MPH. Possible causes are:

• Leak in exhaust system.
• Faulty A/F sensor.
• Open or short in A/F sensor circuit.
• Faulty heated oxygen sensor No. 2.
• Open or short in heated oxygen sensor No. 2.
• Faulty catalytic converter.