Outline Of Diagnosis

WARNING: This page is about a different car, the 2020 Subaru Impreza. However, it is still accessible from the selected car via links, so may be relevant.

Detect the malfunction of transmission forward/reverse clutch pressure solenoid and hydraulic circuit characteristics (stuck to low pressure side).
Judge as NG if the value calculated by "turbine speed - primary pulley speed" becomes the predetermined value or more, even though the forward/reverse clutch is engaged.