Circuit Description

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

HO2Ss are used to minimize amount of time required for closed loop fuel control operation and to allow catalyst monitoring. HO2S heater greatly reduces amount of time needed for fuel control sensors Bank 1 HO2S No. 1 and Bank 2 HO2S 1 to become active. HO2S heaters are needed by post-catalyst monitor sensors to maintain a sufficiently high temperature which allows accurate exhaust/oxygen content readings further from engine. PCM will run a heater test only after a cold start (determined by engine coolant and air intake temperature at time of start-up) only once during an ignition cycle. When engine is started PCM monitors HO2S voltage. When HO2S voltage indicates a sufficiently active sensor, PCM looks at how much time has elapsed since start-up. If PCM determines too much time was needed for Bank 2 HO2S No. 2 to become active, DTC P0161 is set. Time required for HO2S to become active is based on total amount of air that has passed through MAF sensor and into engine (more total airflow equals shorter time to HO2S activity.)

When DTC sets, PCM illuminates MIL on second trip after fault was detected. PCM will store conditions present when DTC was set as freeze frame data in the FAILURE RECORDS data.

PCM will turn MIL off on third consecutive trip cycle during which diagnostic runs and fault is no longer recognized. A history DTC P0161 will clear after 40 consecutive trip cycles during which diagnostic runs and fault is no longer recognized. DTC can be cleared with scan tool, or by disconnecting battery voltage feed to PCM.