Warning Buzzer does not Sound: Description
WARNING: This page is about a different car, the 2008 Toyota Yaris. However, it is still accessible from the selected car via links, so may be relevant.
The combination meter assembly controls the buzzers in accordance with signals from the center airbag sensor assembly, the main body ECU and the taillight relay.
HINT:
The main body ECU receives signals from the center airbag sensor assembly and transmits them to the combination meter assembly.