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 AdjusterAutomatic Transaxle Fluid (ATF) Inspection [FS5 A EL]
Automatic Transaxle Fluid (ATF) Condition Inspection
1. One way of determining whether the transaxle should be disassembled is by
noting:
If the ATF is muddy or varnished.
If the ATF smells strange or unusual.
ATF Condition
Possible cause
...
Front Seat Belt Pretensioner and Load Limiting Systems
For optimum protection, the driver and
front passenger seat belts are equipped
with pretensioner and load limiting
systems. For both these systems to work
properly you must wear the seat belt
properly.
Pretensioners:
When a collision is detected, the
pretensioners deploy simultaneously wit ...
System
The system operates only when the driver
is in the vehicle or within operational
range while the key is being carried.
NOTE
When the battery power is low, or in
places where there are high-intensity radio
waves or noise, the operational range
may become narrower or the system may
not operate ...