Circuit Description - DTC P3115 - Information Codes 231, 232, 233: Notes
WARNING: This page is about a different car, the 2002 Toyota Prius. However, it is still accessible from the selected car via links, so may be relevant.
If the system main relay is deposited, it might be impossible to shut down the high voltage system. Therefore, the HV ECU checks the system main relay and stops the system if malfunction is detected.