Entry Interior Alarm does not Sound: Procedure

WARNING: This page is about a different car, the 2010 Toyota 4Runner. However, it is still accessible from the selected car via links, so may be relevant.

CHECK COMBINATION METER ASSEMBLY (OPERATION)
1. Turn the engine switch on (IG). Place a weight of 20 kg (44.0 lb) on the passenger seat to cause the passenger seat belt warning light to blink.
2. When driving the vehicle at 15 km/h (9.3 mph) or more, check that the seat belt warning buzzer sounds to inform that the passenger seat belt is not fastened.
  HINT:
  
  The smart key system sounds the buzzer built into the combination meter for indoor warnings. This buzzer is also used for the seat belt warning system. Therefore, the operation of the combination meter buzzer can be checked by checking if the buzzer sounds to inform that the seat belt is not fastened.
  
  OK
  
  Combination meter buzzer sounds.
NG → See step 2

OK → See step 3
GO TO METER / GAUGE SYSTEM. Refer to HOW TO PROCEED WITH TROUBLESHOOTING
REPLACE CERTIFICATION ECU. Refer to REMOVAL