I have never used the remote to lock/unlock my car.

After reading your post I replaced the 2 batteries (they were not dead) inserted key in ignition to reengage the sync …….and checked it out.
* the key fob flashes 3 times when depressing the lock button
* the key fob flashes once when unlocking
BUT nothing effects the door or trunk lock

the key WILL unlock the doors - the Dash lock/unlock toggle WORKS for doors and trunk

PROBLEM : with key in- hand while outside the car I cannot lock the trunk !!

Any suggestions ?