System Outline
WARNING: This page is about a different car, the 2008 Lexus SC 430. However, it is still accessible from the selected car via links, so may be relevant.
In the daytime running light system, when the system recognizes that the vehicle is ready to travel according to the signals from the generator and parking brake SW etc., the headlight (High) comes on dimmed through the communication control among the gateway ECU, J/B ECU and front controller etc.