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.

PCM monitors Heated Oxygen Sensor (HO2S) activity for 90 seconds after closed loop operation has been enabled. During this test period, PCM counts number of times HO2S signal voltage crosses rich-to-lean and lean-to-rich threshold. If PCM determines that HO2S switching was insufficient, DTC P1134 will set. A lean-to-rich switch is determined when HO2S voltage changes above and below 450 millivolts. With this information, an average time for all transition can be determined. PCM divides rich-to-lean average by lean-to-rich average to obtain a ratio. If HO2S ratio is not within this range, DTC P1154 will set, indicating HO2S is not responding as expected to changes in exhaust oxygen content.

When DTC sets, PCM illuminates MIL on second trip after fault was detected. Vehicle will operate in Open Loop fuel control. 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 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.