Post Catalyst Fuel Trim System Description/Monitoring Procedure
WARNING: This page is about a different car, the 2011 Suzuki SX4. However, it is still accessible from the selected car via links, so may be relevant.
The ECM monitors the A/F sensor characteristic offset by monitoring the feedback condition of HO2S. When the sum of correction factor of HO2S system exceeds higher or lower value, the ECM will set DTC.