Circuit Description

ECM compares waveform of heated oxygen sensor No. 1 (located before catalytic converter) with waveform of heated oxygen sensor No. 2 (located after catalytic converter) to determine if catalytic converter performance has deteriorated. If both waveforms change at similar rate, catalytic converter performance has deteriorated. DTC P0420 is set when all heated oxygen sensor bank No. 1, sensors No. 1 and 2 waveforms have same amplitude after vehicle is driven for 5 minutes at 20-50 MPH. DTC P0430 is set when all heated oxygen sensor bank No. 2, sensors No. 1 and 2 waveforms have same amplitude after vehicle is driven for 5 minutes at 20-50 MPH. Possible causes are:

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