I'm guessing that before the lock completely stopped working you used to hear a zip/humming like noise when the door locks were activated. That is typically due to the lock servo failing within the door latch assembly. Chances are quite good if you replace the left rear door latch assembly within the door your lock will work properly again.
I think the lock motor is integrated in to the latch assembly on the Pilot but you'll want to confirm that first.
-Rod