1. Measure the temperature around the cabin temperature sensor.
2. Measure the resistance between terminals of the cabin temperature sensor.

Cabin temperature sensor removal/installation
Evaporator temperature sensor removal/installationMazda 6 Service Manual: Disconnection of the negative battery cable
Before beginning any work, turn the ignition switch to LOCK position,
then disconnect the negative battery cable and wait for more than 1 minute
to allow the backup power supply of the SAS unit to deplete its stored
power. Disconnecting the battery cable will delete the memories of the
...
Mazda 6 Service Manual: Smart City Brake Support (SCBS)
The Smart City Brake Support (SCBS) system alerts the driver of a possible collision
using an indication in the display and a warning sound when the Forward Sensing
Camera (FSC) detects a vehicle ahead and determines that a collision with a vehicle
ahead is unavoidable while the vehicle is bei ...