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. While in closed loop, PCM monitors Bank 1 HO2S No. 1 and Bank 2 HO2S No. 1 signals and adjusts fuel delivery based on HO2S signal voltages. Changes made to fuel delivery will be indicated by long and short term fuel trim values that can be monitored with a scan tool. Ideal fuel trim values are about zero percent. If HO2S signals are indicating a lean condition, PCM will add fuel resulting in fuel trim values of more than zero percent. If a rich condition is detected, PCM will reduce fuel delivery resulting in fuel trim values of less than zero percent. If an excessively lean condition is detected on Bank 2, DTC P0174 will set. The PCMs maximum authority to control long term fuel trim allows a range between -15 and 20 percent (automatic transmission) or -12 and 20 percent (manual transmission). PCM monitors fuel trim under various engine speed/load fuel trim cells before determining status of fuel trim diagnostic.

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 P0174 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.