Circuit Description - DTC P3120 - Information Codes 239, 240, 241, 242: 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.
The HV ECU detects the malfunction of the transmission system. Judging from a malfunction symptom, it records one of the four information codes.