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: Foreword
When the customer reports a vehicle malfunction, check the malfunction
indicator lamp (MIL), HOLD indicator light flashing, and PCM memory for
diagnostic trouble code (DTC), then diagnose the malfunction according to
following flowchart.
- If the DTC exists, diagnose the applicable ...
Mazda 6 Owners Manual: System wiring diagram
ABS (ABS/TCS)
DSC
FOREWORD
Before performing the steps in Symptom Troubleshooting, perform the
On-board Diagnostic Inspection. To check the DTC, follow the DTC Inspection
steps.
...