Right rear door lock doesn't always work. Please help.

[Signe]

Left rear door lock doesn't always work. Please help.

When I use my key fob to (remotely) open my door(s), the left rear button doesn't always pop up. The other three are fine. The door will open if I manually pull the button up from the inside, though.

What's causing this? Although I have a bunch of tools and some mechanical know-how to fix it myself, I thought I'd seek some opinions before I remove the inner door panel. Thanks!

P.S. If you happen to have the part number (or know the name of the part that needs to be replaced), that would be great.

 

[LibertyTC]

From Factory Manual:
DIAGNOSIS AND TESTING - DOOR LOCK MOTOR
The most reliable, efficient, and accurate means to
diagnose the power lock system requires the use of a
DRBIIIt scan tool and the proper Diagnostic Procedures
manual. The DRBIIIt scan tool can provide
confirmation that the PCI data bus is functional, that
all of the electronic modules are sending and receiving
the proper messages on the PCI data bus, and
that the power lock motors are being sent the proper
hard wired outputs by the door modules for them to
perform their power lock system functions.
Take it to dealer as above or chance to Pull the door panel and clean contacts & or replace the door lock motor.