1. Remove the climate control unit.
2. Inspect for continuity between the fan switch terminals using an ohmmeter.


Climate control unit inspection
Defroster switch inspectionMazda 6 Service Manual: Jam-safe Moonroof
If a person's hands, head or an object blocks the moonroof while it is closing,
the moonroof will stop and move in the reverse direction.
WARNING
Make sure nothing blocks the moonroof just before it reaches the fully closed
position: Blocking the moonroof just before it reaches the closed posi ...
Mazda 6 Service Manual: Lane Departure Warning
If the system determines that the vehicle may deviate from its lane, the lane
departure warning (beep sound, rumble sound*1, or steering wheel vibration) is activated
and the direction in which the system determines that the vehicle may deviate is
indicated in the multi-information display and ...