TCM Power Source Circuit [09/2023 - ]: Description
WARNING: This page is about a different car, the 2024 Lexus TX 500h. However, it is still accessible from the selected car via links, so may be relevant.
When the ignition switch is turned to ON, auxiliary battery voltage is applied to terminal MREL of the hybrid vehicle control ECU assembly through the coil of the IGCT NO. 1 relay. This causes the ECT-MAIN relay to close, which supplies power to terminal +B of the TCM.