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.

To provide best possible combination of driveability, fuel economy and emission control, a closed loop air/fuel metering system is used. When the vehicle is first started, PCM controls fuel delivery in open loop, ignoring Heated Oxygen Sensor (H02S) signals and calculates air/fuel mixture ratio based on inputs from the Engine Coolant Temperature (ECT), Throttle Position (TP) and Mass Air Flow (MAF) sensors. PCM will begin using Bank 1 HO2S No. 1 and Bank 2 HO2S 1 signals to control fuel delivery under closed loop conditions when following have been met:

HO2S output signals are varying, indicating that sensors are hot enough to operate properly.
ECT sensor indicates coolant temperature above 122°F (50°C).
Time since start-up is at least 16 seconds for a warm engine, or 23 seconds for a cold engine.

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 P0125 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.