Purge control solenoid valve stuck open fault diagnosis
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.
DTC
P0457 Evaporative Emission Control System Leak Detected (Fuel Cap Loose/Off) Purpose of Mode Z
When performing the leakage diagnosis of EVAP system, the purge control solenoid valve must operate normally. Therefore, mode Z is used to diagnose the purge control solenoid valve stuck open condition. Note that if a purge control solenoid valve stuck open fault is detected, the EVAP system leakage diagnosis is cancelled.