My single button remote with the folding slab key has recently stopped locking my car. I tried the synchronizing method mentioned on other posts but that did not help. I have gone through a series of tests and was wondering if anyone can diagnose the problem:

1) pointing the remote at the rear view mirror and pressing the remote button, the red light blinks on the mirror a click is heard the alarm arms itself but the door locks to not lock.
2) pressing the remote again a click is heard , green light on mirror flashes the alarm disarms.
3) using the slab key in the passenger door which is the only door with cylinder, the passenger door locks a click is heard and the alarm arms itself no other doors lock.
4) using slab key again the alarm goes out and passenger door opens.
5) pushing all locks down manually and then using the slab key to lock passenger door all doors are now locked and alarm is armed.
6) using the REMOTE to open the doors by pointing at the mirror BOTH FRONT doors now open and the alarm disarms. The back doors do not unlock.

Any help would be appreciated THANKS Rod