DTC P2610: ECM / PCM Internal Engine Off Timer Performance [08/2013 - ]: Description
WARNING: This page is about a different car, the 2014 Lexus ES 300h. However, it is still accessible from the selected car via links, so may be relevant.
The soak timer operates after the power switch is turned off. When a certain amount of time has elapsed after turning the power switch off, the soak timer activates the ECM to perform malfunction checks which can only be performed after the engine is stopped. The soak timer is built into the ECM.