I've been having problems with locking my 2011 4S with the key fob for a while now. At first it was just an occasional hiccup that surfaced for a day or two and then disappeared for weeks/months, then it started occurring more often but still went away after a few occurrences. Now, it appears to be more often, I isolated it down to the driver's side rear door and found that if I manually activated the locking actuator by turning the switch accessed behind the cover on the door jam (I made that hole to access the switch)

that I could get the door to lock with the key fob and allow the system to arm the alarm (without that, the alarm still activates but that door will not lock and the alarm will not signal with the customary double beep). I noticed that I got a "key battery low" message when I inserted the key. I checked the key fob battery and it was at 3.04VDC which for a CR2032 battery is good but I changed it anyway, the new battery is measuring 3.24VDC and now the system seems to be locking correctly. I don't see how this could be the reason for the issue but again, the system is really being squirrely so I don't know what to make of it. The lock actuators should either work or not work and they seem to be intermittent and sort of sharing the issue. The rear driver's side had been the issue and then the passenger's side front door started having problems along with it. I checked the fuses and they are all good and I cleaned the contact surfaces just to be safe. I quess I will find out if the new fob battery clears the issue (I sort of doubt it but at this point, who knows?). I love this car and it is mechanically sound but the electronic systems seem to be the weak point as the car ages.