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 AdjusterMazda 6 Owners Manual: Dtc b1318
Caution
When attaching the tester lead to the ABS (ABS/TCS) HU/CM harness
connector, the SST (49 G066 001) must be used. (See ABS (ABS/TCS) HU/CM
INSPECTION.)
Diagnostic procedure
...
Mazda 6 Owners Manual: Rear center seat belt removal/installation
Caution
The ELR has a spring that will unwind if the retractor's cover is
removed. The spring cannot be rewound by hand. If this occurs, the ELR will
not work properly. Therefore, do not disassemble the retractor.
4SD
1. Fold the rear seat back.
2. Remove the rear package trim.
3. Re ...