Ever since I've owned my Impala, the doors have locked automatically when I put the car in gear, which I think is a default setting because every GM car I've owned in the past 20 years or so has done this. But a few days ago, and for no apparent reason, that behavior changed. Now, the doors lock the instant I start the car. It'* not a big deal, but it is a little annoying. I know the door lock behavior can be customized on most GM cars made in the past 20 years or so--I programmed the five-second delay into a '97 Olds LSS I had a few years ago--but I don't recall consciously doing anything to reprogram my lock behavior. It'* been very hot here the past few days, so I haven't felt like sweltering in the driveway to try and figure this out, but I do plan to sit in my air conditioned house today and read the owner'* manual to find out what I need to do to get it back to its 'regular scheduled programming' and hopefully the gremlins will leave it alone.

I took a skim through the manual, and the manual offers the following info on this:
This suggests that this behavior is absolute, and cannot be changed. The DIC does offer a wide variety of automatic unlock options, but nothing to change the locking behavior.

If I had to guess, there is a problem with something on the vehicle, causing the locks to behave as if it is not in park when the key is on, but not so much so that it is preventing startup or causing other issues.

I am thinking the best move may be to try and track it down with a Tech II, which would mean dragging it straight to a dealership, assuming it is enough of a concern to you that you want to get it fixed.

Thanks. You could be onto something there. I had a car once--don't remember which one--that sometimes wouldn't start because it thought it wasn't in Park. When that would happen, I had to bang the shift lever forward a time or two to convince it.

I don't have a TECH II device, but I do have a generic OBD II scanner. I'll see if it turns up any helpful codes.

The door locks are becoming more erratic now. I went to pick a friend up this evening and while I was waiting in her driveway, I opened the driver'* door and the locks immediately cycled and the horn gave three short beeps. It did the same thing when I opened the door a few minutes later. That behavior reminds me of when I've programmed remotes on mid-late '90s GM cars with the jumper wire method. Several times while I was driving this evening, the doors tried to lock spontaneously while going down the road, even though they were already locked. The capper was when I got home and parked in the driveway. I put the car in Park and the locks opened as they should, then as I tried to open the driver'* door to get out, it spontaneously locked back, then unlocked again. Weird... Oh, and I ran my OBD II scanner on the car this afternoon but it didn't throw any codes.

Your scanner probably only reads "P" codes....you need to read "B" codes....

I think your problem comes down to one of two things.....

One wiring problem, especially a chafed wire.....

And two....I am leaning towards, a bad body control module.....BCM....

My 'possessed' door locks seem to have settled down lately (hope I didn't just jinx it by saying that) but they do occasionally spontaneously try to cycle, usually when I go over a bump or take a sharp left turn. And that'* got me thinking. Where is that BCM module located? Shortly before all this started, I replaced a blend door actuator--the one on the far right that controls the fresh air/recirculate door, and the old actuator fell down where I couldn't reach it. Could it be sitting on top of the BCM and somehow be causing this issue?

Wow, blast from the past. The door locks settled down for several months and then briefly acted up again about three weeks ago when I was leaving work. I stopped off for gas on the way home and it was fine again once I got back under way.