Circuit Description

ECM monitors heated oxygen sensor No. 2 located after catalytic converter to determine if converter performance has deteriorated. If converter is functioning properly, heated oxygen sensor waveform switches back and forth between rich and lean more slowly. DTC is set when A/F sensor and heated oxygen sensor No. 2 have same amplitude after vehicle is driven for 5 minutes at 20-50 MPH. Possible causes are:

• Exhaust system leak.
• Defective Air/Fuel (A/F) Sensor.
• Defective heated oxygen sensor No. 2.
• Defective catalytic converter.