Diagnostic Method 1: Notes
WARNING: This page is about a different car, the 2012 Subaru Forester. However, it is still accessible from the selected car via links, so may be relevant.
Detect the malfunction depending on the average value of time necessary for λ to inverse the air fuel ratio from "Lean → Rich → Lean" to "Rich → Lean → Rich".
Courtesy of SUBARU OF AMERICA, INC.