Depress the button on the seat belt buckle.
If the belt does not fully retract, pull it out and check for kinks or twists. Then make sure it remains untwisted as it retracts.

NOTE If a belt does not fully retract, inspect it for kinks and twists. If it is still not retracting properly, have it inspected at an Authorized Mazda Dealer.
Fastening the Seat Belt
Front Shoulder Belt AdjusterDrive Shaft Inspection
1. Inspect the connections for any looseness.
If there is any malfunction, tighten or replace the applicable part.
2. Inspect the dust boot for damage and cracks.
If there is any malfunction, replace the applicable part.
3. Move the spline and joint up and down, left ...
Crankshaft Position (CKP) Sensor Inspection [Mzr 2.0, Mzr 2.5]
Visual Inspection
CAUTION:
When foreign material such as an iron chip is on the CKP sensor, it can cause
abnormal output from the sensor because of flux turbulence and adversely affect
the engine control. Be sure there is no foreign material on the CKP sensor when
replacing.
...
Air Bag/Front Seat Belt
Pretensioner System Warning
Beep
If there is a problem with the air bag/seat
belt pretensioner systems and the warning
light illumination, a warning beep sound
will be heard for about 5 seconds every
minute.
The air bag and seat belt pretensioner
system warning beep sound will continue
to be heard for approximately 35
min ...