1. Verify that the joint shaft is not twisted or cracked.
2. Turn the joint shaft by hand and verify that the bearing rotates smoothly and freely.

Drive shaft
Joint shaft removal/installationMazda 6 Service Manual: Variable tumble control system (vtcs) shutter valve actuator inspection
1. Remove the air hose. (See INTAKE-AIR SYSTEM REMOVAL/INSTALLATION.)
2. Disconnect the vacuum hose from the VTCS shutter valve actuator.
3. Connect a vacuum pump to the VTCS shutter valve actuator.
4. Apply vacuum and verify that the rod moves.
If the rod dose not move, replace the intake ...
Mazda 6 Service Manual: No.2 air bag system warning light is illuminated all the time
Diagnostic Procedure
When performing an asterisked (*) troubleshooting inspection, shake the
wiring harness and connectors while doing the inspection to discover whether
poor contact points are the cause of any intermittent malfunction. If there
is a problem, check to make sure connec ...