Post Catalyst Fuel Trim System Description/Monitoring Procedure
WARNING: This page is about a different car, the 2006 Suzuki Grand Vitara. However, it is still accessible from the selected car via links, so may be relevant.
The ECM monitors the A/F sensor A/F characteristic offset by monitoring the feedback condition of O2 sensor. When the sum of correction factor of O2 sensor system excess higher or lower value, the ECM will set DTC.