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 accurate catalyst monitoring. HO2S greatly decreases amount of time needed for Bank 1 HO2S No. 1 and Bank 2 HO2S No. 1 to become active. HO2S are required by post-catalyst monitor sensors to maintain sufficiently high temperature which allows accurate exhaust/oxygen content readings further from engine. PCM will run heater test only after cold start (determined by engine coolant and intake air temperature at the time of start-up) and only once during each 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 1 HO2S No. 1 to become active, DTC P0135 is stored. Amount of time HO2S should take to reach operating temperature is based on accumulated amount of air that has passed through MAF sensor and into engine (More total air flow 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 P0135 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.