Driver Side Seat Belt Warning Light does not Operate [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 combination meter assembly illuminates, blinks or turns off the seat belt warning light on the combination meter assembly in accordance with the state of the front seat inner belt assembly LH.
HINT:
The seat belt warning light on the combination meter assembly is used for both the driver seat and front passenger seat.