Circuit Description

The ECM compares waveform of oxygen sensor located in front of catalytic converter with the waveform of oxygen sensor located behind converter to determine if converter performance has deteriorated. If converter is functioning properly, waveform of oxygen sensor after converter will switch back and forth between rich and lean much more slowly than waveform of oxygen sensor in front of converter.

DTC is set if after driving vehicle for 5 minutes at 20-50 MPH and engine is at normal operating temperature, oxygen sensor waveforms are the same. Possible causes are:

• Catalytic converter.
• Open or short circuit in oxygen sensor circuit.
• Oxygen sensor.