These locks are intended to help prevent children from accidentally opening the rear doors. Use them on both rear doors whenever a child rides in the rear seat of the vehicle.
If you slide the child safety lock to the lock position before closing that door, the door cannot be opened from the inside.
The door can only be opened by pulling the outside handle.

Locking, Unlocking with Door-
Lock Knob
Doors and LocksABS HU/CM Inspection
1. Disconnect the ABS HU/CM connector..
2. Connect the negative battery cable..
3. Attach the tester lead to the ABS HU/CM wiring harness-side connector and
inspect the voltage, continuity, or resistance according to the standard (reference
value) in the table below.
Standard (reference)
...
Fuel Injector Inspection [Mzr 2.0, Mzr 2.5]
Resistance Inspection
1. Remove the battery cover..
2. Disconnect the negative battery cable..
3. Disconnect the fuel injector connector.
4. Inspect the resistance between fuel injector terminals A and B.
Fuel injector resistance
11.4—12.6 ohms [20 °C {68 °F}]
If ...
Contact Authorized Mazda Dealer and Have Vehicle Inspected
If any of the following warning lights or the indicator light turns on/flashes, the system may
have a malfunction. Contact an Authorized Mazda Dealer to have your vehicle
inspected.
...