DOOR UNLOCK mechanism not engaging sometimes preventing door access IN or OUT

What is your question?

have 2 PARK AVE's..both 02 modl yrs. each has experienced same issue in past yr where the UNLOCK MECHANISM disengages and prevents door access in or out. 1 happened on driver side dr, other on passenger side. sometimes it operates fine. no consistency to occurrance regardless of hot or cold outside temps. where's part located and how is it fixed?