Doors spontaneously lock with engine on or off.
 

Just started in the past two days. Doors will spontaneously lock. Discovered it this AM when i went to get in the car in the garage. It was locked. Then, at the mall, i unlocked the car to put stuff in the hatch but then when I went to open the driver door, it was locked. Unlocked the car and got in and seconds later the door locked. was able to unlock with both the remote and the electric door switches but it would lock again. In fact, for a while it attempted to lock the doors several times in 30 seconds. Did the same thing when the car was running (and the remote is not operable when the car is running) We have had some cold weather (was -14F last week) and today it is warmer and damp (34F) Garage is usually about 60F. Did not happen as much on the drive home but it still self locked. Thoughts?

On my 08 there is a "safety" system, with which if you unlock the car, and don't open a door within a few seconds, it will re-lock itself.

Perhaps you have this installed, and something is confusing it to give random "lock-all" commands.
Without knowing the specifics of the circuit schematics it's difficult for me to say, but there may be a time-delay relay in the locking circuit for this purpose, which is somehow getting a permanent (or near permanent) input to it's coil, so once it times out, it sends the signal to lock. Have a look for a TDR, and if you find one, pull it out (with the car unlocked and windows down just in case), and see if you can still lock and unlock with the remote.
If you can, this may alleviate the symptom, but not cure the problem.

If there's no relay for it, and the computer is directly connected to the locking solenoid, then it's a computer issue, and you'd need to know the inputs & programming to do much more there.

Sorry if it's not much help.

As it turns out, it stopped happening within a couple of days. I suspect it had something to do with the rapid weather change and the humidity and, like you said, the automatic locking mechanism gone awry. Thanks for getting back to me.

i had a pontiac that would do the same thing. tried to automatically lock the doors even though it was already locked and shut off. eventually it would go all night long the car wouldnt start in the morning. the mechanics couldnt find the problem, except to remove the auto locking mechanism. they suspected it was a fuse, checked, replaced, but it kept doing it. then they assumed it was faulty and i didnt want to spend more money replacing it, so they just took it out for me.

I have an '05, but check your service manual/owners manual, your explanation might be there. Where are you located/climate?