I have a 2006 Forester, The remote control is not operating reliably The "lock function" works part of the time, and the "unlock" function has stopped working altogether. I don't know if the problem is with the hand held key fob remote  or the receiver in the car. I have a second factory key fob remote which came with the car and has never been used. How do I "syn" the second key fob to the receiver in the car? Thanks.

 

Cars101.com has instructions for this.

 

Many times a weak transmitter battery will cause intermittent/strange operation of the remotes. Usually the battery can be replaced without having to reprogram the remote.