Meter Illumination is Always Dark: Description

WARNING: This page is about a different car, the 2009 Lexus IS 350 and 2009 Lexus IS 250. However, it is still accessible from the selected car via links, so may be relevant.

In this circuit, the meter CPU receives auto dimmer signals from the main body ECU RH using the BEAN lines.
When the meter CPU receives an auto dimmer signal, it dims the meter illumination.
The main body ECU RH determines whether it is daytime, twilight, or nighttime based on the waveform transmitted from the automatic light control sensor.
If the main body ECU RH determines that it is daytime, the ECU does not send auto dimmer signals.
Therefore, the meter illumination (warning and indicator lights) will not dim even if the driver accidentally turns the light control switch to the TAIL or HEAD position in daytime.