Circuit Description

WARNING: This page is about a different car, the 2002 Toyota Avalon. However, it is still accessible from the selected car via links, so may be relevant.

Engine Control Module (ECM) monitors waveform pattern of heated oxygen sensor (bank No. 1 sensor No. 2) located behind catalytic converter to determine if catalytic converter performance has deteriorated. 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 heated Air/Fuel (A/F) sensors. A/F sensors may also be referred to as A/F ratio sensors. If both waveform patterns switch at a similar rate, catalytic converter performance has deteriorated. DTC is set when A/F sensors 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.