1. Remove the rear door unit.
2. Remove the screws, then remove the rear door latch and lock actuator.

3. Install in the reverse order of removal.
Front door latch and lock actuator removal/installation
Front door key cylinder removal/installationMazda 6 Service Manual: Indication on Display
The Distance Recognition Support System (DRSS) operation status is indicated
in the active driving display or multi-information display. Regarding malfunctions,
check the vehicle conditions or have it inspected by an Authorized Mazda Dealer
according to the content of the displayed message.
R ...
Mazda 6 Service Manual: Operation
NOTE
The engine may not start and security indicator light may illuminate
or flash if the key is placed in an area where it is difficult for the system
to detect the signal, such as on the dashboard or in the glove compartment.
Move the key to a location within the signal range, switch ...