ECM 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, the auxiliary battery voltage is applied to IGP of the ECM. When the transistor in the MREL circuit operates, current flows from the auxiliary battery to ground through the drive circuit of the EFI-MAIN NO. 1 relay, thus operating the relay which supplies power to the +B, +B2 and +B3 terminals of the ECM.