Outline Of Diagnosis

WARNING: This page is about a different car, the 2022 Subaru WRX. However, it is still accessible from the selected car via links, so may be relevant.

Detect the short circuit to ground in transmission forward/reverse clutch pressure solenoid circuit.
Judge as NG when an abnormal signal is received from the solenoid driver IC of the transmission forward/reverse clutch pressure solenoid drive circuit.