Hello,
here is what is happening.
2008 vanden plas
The driver rear door does not unlock or lock with any of the following.

• Fob
• Lock button
• When the car automatically locks/unlock when the car is put in park.

I hear a whirling sound when it's supposed to lock/unlock. The lock can be moved manually.

Any help with troubleshooting and solutions are much appreciated.

 

Can you expand on what you mean by moving the lock manually.

Do you mean that you are able to lock/unlock the door using the interior chrome lever/button?

 

Correct. If I disengage the lock by moving the button. The door will open with both the inside and outside handle

 

In my experience locks fail when the microswitch in the actuator fails but

in your case because you can hear a noise when you try to lock the door,

with the fob for example, I can say that the microswitch is still working.

I assume that all other doors lock/unlock normally hence the problem is

probably still related to the rear door actuator and /or it's connecting cable.

I suggest that you need to investigate the cable connection first since

people have reported cases where the cable has been too tight preventing the

actuator from working properly.

Wiring and plug/socket problems are possible but unlikely.

If there is nothing out of place you may need to replace the actuator.