Because the antenna system is equipped with a capacitor, the continuity cannot be checked. Therefore proceed the following simple inspection.
Turn the AM radio on.
Tune to the frequency that there is no broadcast and you will hear a buzzing sound.
Turn a work light on and shake it around the antenna rod. (around 10—20 mm {0.40—0.78 in})
CAUTION:
Use a fluorescent light type for the inspection. Accurate diagnostic cannot be done with a different type of light.

If a whirring sound from the speaker synchronized to the work light movement is confirmed, the antenna system is normal.
Coil Antenna Removal/Installation
Entertainment Personalization Features Setting ProcedureOn Board Diagnostic System PID/Data Monitor Inspection [FS5 A EL]
NOTE:
The PID data screen function is used for monitoring the calculated value
of input/output signals in the module. Therefore, if the monitored value of
the output parts is not within the specification, it is necessary to inspect
the monitored value of input parts corresponding to ...
Error Indications (Type A)
If you see an error indication on the
display, find the cause in the chart. If you
cannot clear the error indication, take the
vehicle to an Authorized Mazda Dealer.
Indication
Cause
Solution
CHECK
USB
USB device
malfunction
Verify that the content
...
No.2 Car Navigation System Does Not Operation [Car Navigation System]
2
Even if the map screen is touched, the car-navigation system cannot be
operated
Possible DTC
—
POSSIBLE CAUSE
Audio unit malfunction (bad LCD panel)
Car-navigation unit malfunct ...