Circuit Description

Engine Control Module (ECM) compares waveform pattern of Air/Fuel (A/F) sensor (bank No. 1, sensor No. 1) with waveform pattern of heated oxygen sensor (bank No. 1, sensor No. 2) below catalytic converter to determine if catalytic converter performance has deteriorated. A/F sensor and heated oxygen sensor are located on exhaust manifold above catalytic converter. See Figure. Air/fuel ratio compensation keeps the waveform pattern of A/F sensor repeatedly switching back and forth from rich to lean. If catalytic converter is functioning properly, the waveform pattern for heated oxygen sensor (bank No. 1, sensor No. 2) should switch back and forth from rich to lean more slowly than A/F sensor (bank No. 1, sensor No. 1). If both waveform patterns switch at a similar rate, catalytic converter performance has deteriorated. DTC is set when A/F sensor (bank No. 1, sensor No. 1) and heated oxygen sensor (bank No. 1, sensor No. 2) have nearly the same waveform pattern after engine and catalytic converter are at normal operating temperature and vehicle is driven. Possible causes are:

• Exhaust system leak.
• Defective A/F sensor.
• Defective heated oxygen sensor.
• Defective catalytic converter.