Circuit Description

ECM compares waveform of heated oxygen sensor located in front of catalytic converter with waveform of heated oxygen sensor 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 both oxygen sensors have same amplitude after vehicle is driven for 5 minutes at 20-50 MPH. Possible causes are:

• Exhaust system leak.
• Heated oxygen sensor circuit is open or shorted.
• Defective heated oxygen sensor.
• Defective catalytic converter.