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 > Vacuum Warning Switch: On-vehicle Inspection
ON-VEHICLE INSPECTION
PROCEDURE
1. INSPECT BRAKE FLUID LEVEL IN RESERVOIR
Click here
2. INSPECT BRAKE BOOSTER ASSEMBLY
Click here
3. REMOVE OUTER COWL TOP PANEL SUB-ASSEMBLY
Click here
4. INSPECT VACUUM WARNING SWITCH ASSEMBLY
(a) Start the engine and stop it after 1 or 2 minute ...
Toyota CH-R Service Manual > Tire Pressure Warning System: Tire Pressure Monitor Receiver Communication Stop (B1247)
DESCRIPTION
The main body ECU (multiplex network body ECU) and tire pressure warning ECU
and receiver are connected using 2 direct lines that they use to communicate with
each other.
DTC No.
Detection Item
DTC Detection Condition
Trouble Area
...