The Blind Spot Monitor is a system that has 2 functions;
These functions use same sensors.

RCTA function: When a vehicle approaching from the right or left at the rear of the vehicle is detected, both outside rear view mirror indicators will flash.
Turning the BSM function/RCTA function on/offToyota CH-R Service Manual > Blind Spot Monitor System: Customize Parameters
CUSTOMIZE PARAMETERS
CUSTOMIZE BLIND SPOT MONITOR SYSTEM
(a) Customizing with the Techstream
NOTICE:
When the customer requests a change in a function, first make sure that
the function can be customized.
Be sure to make a note of the current settings before customizing.
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Toyota CH-R Service Manual > Meter / Gauge System: Problem Symptoms Table
PROBLEM SYMPTOMS TABLE
NOTICE:
When replacing the combination meter assembly, always replace it with a new one.
If a combination meter assembly which was installed to another vehicle is used,
the information stored in it will not match the information from the vehicle and
a DTC may be stored ...