1. Inspect the dust boot on the drive shaft for cracks, damage, leaking grease, and looseness in the boot band.

2. Inspect the drive shaft for bends, cracks, and wear in the joint or splines.
Joint shaft disassembly/assembly
Drive shaft removal/installationMazda 6 Service Manual: Rear door lock actuator inspection
Door Lock Actuator
1. Disconnect the front door lock actuator connector.
2. Apply battery positive voltage to the front door lock actuator terminals
and inspect the operation of the front door lock actuator.
If not as specified, replace the front door lock actuator.
With double locking ...
Mazda 6 Service Manual: Battery Recharging
NOTE
Before performing maintenance or recharging the battery, turn off all
accessories and stop the engine.
To disconnect the battery, remove the negative cable first. Install it
last when connecting the battery.
Be sure to remove the caps before recharging the battery.
I ...