Cant really say, in other words, you don't get to know the problem until you use it. So with the other manufacturers, it could be something really weired. However, I have discovered some causes that might be responsible for the central locking issues in toyota camry. 1) If in the event the remote cell is dead or low power, it would definitely open the doors but, the emitted frequency is not powerful enough to actually perform the close function. Weired, but, its true, when you press the button on your remote to say, close the doors, the battery is weak, so the emitted frequency is low, but, still received by the receiver on car, so the receiver is clever enough to think that, the command was to close the doors, but, when it looks into its database for the frequency match, it cannot match the numbers and thus it flashes the light twice and chirps twice to indicate that, the message was received but, I cannot process it. 2) Some people also mentioned that lock function also doesn't work from the master control ie. drivers side controls and also with the keys. Possible reasons are, when the situation 1)(above) occurs, and if by any chance you tried your keys to lock all the doors, the electrical system actually splits itself from the actual mechanism. Results of electrical charge variance. As an effect, doors do not lock from the master control and with the keys as well. Only if you are lucky, the drivers door will lock with the keys, but, rest of the three doors are clue less as they are no longer connected to central bus. The situation in commonly know as Trip system (Trip Wiring), the kind of system used in most houses these days, to prevent short circuit situations. 3) This may be quite common and most mechanics would consider this as the first check point. The Actuators, which help to convert that electrical function of you press the remote button > receiver receives the command > passes the electrical pulse powerful enough to move the piston rod kind of thing on the actuator, to perform the mechanical action of locking the doors. If this actuators are out of alignment, it will also cause fail security system or doors not locking properly/at all. Circumstances when this happen, if you slam the door out of frustration, accident etc. This are more or less my assumptions based on my knowledge around the subject and some of the possible causes as told to me by Toyota motors. Good Luck.
