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 P1133 will set. A lean-to-rich switch is determined when HO2S voltage switches from above to below 450 millivolts. HO2Ss are used to minimize amount of time required for closed loop fuel control operation and to allow accurate catalyst monitoring. Oxygen sensor heater greatly reduces amount of time required for fuel control sensors Bank 1 HO2S No. 1 and Bank 2 HO2S No. 1 to become active. Oxygen sensor heaters are required by post-catalyst monitor sensors to maintain sufficiently high temperatures for accurate exhaust oxygen content readings taken further away from engine.

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.