Circuit Description

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

Engine Control Module (ECM) compares waveform pattern of heated oxygen sensor (bank No. 1 sensor No. 1) located on driver's side exhaust manifold with waveform pattern of heated oxygen sensor (bank No. 1 sensor No. 2) located on driver's side exhaust pipe behind catalytic converter to determine if catalytic converter performance has deteriorated. If catalytic converter is functioning properly, 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 oxygen 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 heated oxygen 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 heated oxygen sensor.
Defective catalytic converter.