My rear passenger door no longer locks/unlocks with the remote or the locking button of the car. This prevents the light from going off for quite a while, as well as making the car insecure. It's also just a hassle when I have to reach back and manually unlock it so that someone can get in. Does anyone have any ideas as to why it has started doing this, and how to fix it? I'd appreciate your help. Thanks.

 

Welcome

This sounds like the door lock actuator.

 

or maybe the door lock solenoid..?

I've got kind of the same problem with my front passenger side door. The switch on the door to manually unlock or lock the door will move a bit but not the full way when using the remote or the power lock button in the car.

I'm counting on taking apart the door panel to try to find a problem in the door but am a little bit reluctunt as I'm afraid I may break something in the process which would cost me lots of money and hardship. Instead, lately I just tell my passengers to sit in the back and if I need to I unlock and lock the door manually.

I hope that helps a little with your door lock problem. Good luck~