Circuit Description

Engine Control Module (ECM) compares waveform pattern of Air/Fuel (A/F) sensor (bank No. 2 sensor No. 1) with waveform pattern of heated oxygen sensor (bank No. 2 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. 2 sensor No. 2) should switch back and forth from rich to lean more slowly than A/F sensor (bank No. 2 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. 2 sensor No. 1) and heated oxygen sensor (bank No. 2 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.