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: Foreword
Outline
There are two on-board diagnostic functions: Operation mode, which
inspects for and indicates correct operation of the input signals to the
control module, and condition detection mode, which indicates troubles in
the system.
The two functions can be done using either of the f ...
Mazda 6 Service Manual: Engine Coolant Temperature Gauge (Without Multi-information Display)
Displays the engine coolant temperature. The white gauge indicates that the engine
coolant temperature is low, and the red gauge indicates that the engine coolant
temperature is high and overheating.
CAUTION
If the engine coolant temperature gauge indicator flashes, there is a possibility
...