Circuit Description

ECM compares waveform of heated oxygen sensor located before catalytic converter with waveform of heated oxygen sensor located after catalytic converter to determine if converter performance has deteriorated. If both waveforms change at similar rate, catalyst performance has deteriorated. DTC is set when both oxygen sensors have same amplitude after vehicle is driven for 5 minutes at 20-50 MPH. Possible causes are:

• Defective catalytic converter.
• Heated oxygen sensor No. 2 circuit is open or shorted.
• Defective heated oxygen sensor No. 2.