When I place the key into the driver's door and turn it manually to lock, only the driver's door responds. (The passenger door, glove box, fuel door, and trunk do not lock)

However, when a place the key into the driver's door and manually unlock the door, the passenger door does respond and unlocks.

That is why I'm thinking it's the passenger door lock itself that's the issue.

Perhaps there's a sensor in the door lock actuator that is not detecting when the door is being locked, and therefor not sending that signal onward so the passenger door, glove box, fuel door and trunk also lock.

Thoughts?