Automatic door locks

Hmm, if memory serves, this is a programmed function, though it's been a while since I've had a Lumina. Looking in Prodemand and AllData won't turn up anything, because they generally focus on bigger issues. But I thought that it was set up where the car would lock automatically when you put it in gear, and unlock when you put it in "park" or something along those lines. As far as disabling the function, there's no known way to do that other than to pull the fuse for the power locks. But that would completely disable the power lock system, so even the fob wouldn't do anything.

As it turns out though, my father-in-law has a 1999 Lumina. I can call him up later on and ask him how his works. That'll shed some light on the mystery.

As far as I remember it's always done this ever since new, and just on startup of the engine. It unlocks when the engine is turned off. Once it's unlocked it stays unlocked after being put in gear. I'll make sure about the 15 mph auto lock, but don't remember having that happen. We just got this a week ago, haven't used it much.
My other (newer) GM vehicles all are programmable via the DIC or arcane combos of key position and pedal/toggle movements.
Mother in law got locked out in an attached garage. By the time AAA got there to unlock it, her house was full of carbon monoxide.
Hopefully a hidden vehicle door key isn't in our future!

Haha about the key. I have a pull string set up on my 2002 blazer that pops the rear glass open. As for my father in laws car, his doesn't auto lock or unlock at all, but the power locks do work when you push the button. I suspect his not functioning might have something to do with the ignition interlock device on his car.

But having it auto-lock when you start the engine is odd. I've never seen a GM do that, and I only buy GMs. I suspect you may just have some sort of odd problem in your car's Body Control Module, the computer that controls such functions. Does your car have any other quirks? Maybe the security light stays on? Or maybe the cruise control doesn't work. Anything like that.

The only other major quirk is I've got a sudden twitch whenever the wife kicks me for looking at some cute 50 year old widow. Just sayin' she says that'd be robbing the cradle! So disrespectful.
But I'll be sure to try out ALL the Lumina's features. So far the cruise control was okay, etc. just the lock issue. It does have the passkey anti theft and chipped key feature.
It truly was only driven to church and the grocery store by an old woman, always kept in a garage, and taken to a decent shop for all scheduled work per the manual. But at 94, unable to walk much, unable to lift her arm to the wheel, or her foot to the brake, she relented and we have it. But only after her blind second husband told her she had plenty of room next to the church's light pole base, .just to push harder on the gas. She did, despite the scraping sounds.
I guess the six foot crease down the right side adds character!
The key fob looks different than any pictured on the web. Working lock/unlock buttons on top, red alarm button on the bottom right (works), a round "GM" button on the bottom left that eventually opens the trunk if it's held down. And a really small dot (1/32"?) right in the center that looks like a "reset" point button. Haven't pushed it yet. May not be anything. GM Corp Customer Service says they cannot look it up using the GM part number on it. That it's too old.

By chance, does the car have an aftermarket security system? Because that would explain a lot of things. To disable that, you'd have to find the guts of the thing and unhook it.

It is an OEM system. I took the car out for a long run in a steady cold rain and tried every function at least twice. It all works, no hesitations or fails. Locking and unlocking the doors with the remote does chirp the horn as on other programmable vehicles. The auto lock feature will trigger after engine start, or with the key in the run position. The auto unlock triggers as the key is moved off of the run position. This occurs in both "park" and "neutral" while moving the key to start or run.
The shift lever is not sloppy. It doesn't change this if the shifter is held firmly against either side of the "park" position . The photo of the key fob shows the little dot in the center. I'm wondering if anybody knows if it has a function. The key fob works okay. The GM button operates the trunk release.
Thanks for the efforts on this.

That key fob is an aftermarket replacement, probably purchased off of Amazon or Ebay for a few bucks. An OE one would say "trunk" on the trunk release button, not "GM." Plus the buttons aren't even a little worn off, like they normally would be on a twenty year old fob. If I had to guess, I'd say that the button in the middle has something to do with syncing it to the car.

As others have told you, I can't seem to put my finger on exactly what's going on. An educated guess would be that it has something to do with the way that fob is programmed to the car. Perhaps re-syncing it would help. Check this video out for instructions: https://www.youtube.com/watch?v=b81j97xZ7PE

And here are actual written instructions: https://blog.keylessentryremotefob.com/2013/12/1999-chevrolet-lumina-key-fob-remote.html

Give it a shot is all I can think of right now.

All this internet stuff is totally magic to old guys like me! But I do believe you!
I will look at your links.
My Mom In law claims it's the only, and original, remote she ever received.
But I'm a tiny bit smart. So I'll never ask her if she's sure. Even though GM usually supplies two remotes on a new car purchase. Just sayin'. .
For now I'll hide an extra door key in a magnetic case somewhere on the body.
Just in case my wife locks herself out.
Sigh.
So this ends up being a wizard challenge for all who wish to help us "common" and "uneducated" peons!
May the "Bookers" be with you.
And thank you.
And be responsible in all ways.

Hate to be the bearer of bad news, but that remote is one of the ones used on a dealer installed "accessory" alarm system, not one that was the built in factory option. The OEM factory installed Lumina remote is the 3 button unit in the attached image.

The dealer installed item was a 4 button remote from Directed Electronics that controlled the DEI after market alarm and key-less entry unit. The small "button" in the center of the remote you have should be a red and green LED that responds differently depending on which options are installed and enabled in the control box. It is somewhat of a generic unit that dealers sold as an upgrade and was installed by them on vehicles that didn't have the factory system or that didn't have an alarm with the factory system to give you key-less entry and an alarm, The 3 second auto-locking option is a DEI common feature. The second image shows a section from a model 425 guide showing that option.

Most of the DEI units have a model and serial number that can be looked up to get instructions on the unit. The OEM units like yours are adapted from one of their consumer models and sold strictly to dealers. They included branded remotes to make them look like a factory item but they really are not. Some used internal switches to select the options, others use a programming switch and the remote to program options and they also had units that used a special programmer box to set the options.
The controller will be installed under the dash, usually tucked up in the wiring or taped in place. It will have 3 to 4 wiring plugs on it that connect it to the vehicle.

DEI has been around a long time, they make the Viper, Python, Auto Start and many more alarm and remote start units. https://www.directed.com/

Wow! Think there is a way for me to get the specific programming instructions for that unit from way back then? I'm wondering about how to just remove it, since it is locking the doors while they're still open. I'll try to find the ID numbers under the dash.
Yesterday I started hearing a single click as the brake is applied or released with the motor running, while in park only. Not at all when out of park. It's very noticable, about where the steering column is, under the dash area.
It's a new noise. Web says is a safety interlock that's getting noisy, not a big deal. Think it's related to this dealer installed remote?

If you can get the information off the unit it should be possible to get the info. DEI is pretty good about support. Removing it is an option but you would need the installation manual to be sure where each wire went. It is piggybacked onto the OEM system but some wires do get cut and if you missed one you could end up with worse problems than locking doors.

The click would be the park interlock solenoid. Keeps you from putting the car into gear without your foot on the brake. You can thank the folks who drove through houses and stores for that item. As they wear the plunger moves a bit farther until you hear the internal stop get louder as the plastic on it wears.

Unless I get those install sheets I wouldn't even think of it. It would go to my brutally honest and not so cheap private repair shop. The guy who told me never wash a motor. Right after he put a new coil into our 2008 Malibu LTZ. After I had cleaned 150,000 miles of previous owner grime away. Sure was clean for him when he fixed it.
I'll just hide a door key on the body of Lumina unless he guarantees me total success.
I'll try the supplier for programming instructions if I do get the numbers off the unit. Maybe reprogramming will fix it.
The Lumina only has about 48,000 on it, so the interlock click is kinda early. I may ask our local wizard if he can replace it. But it's just an aggravating thing it seems.
Thanks for the help from both you guys. I can share experiences on our 2007 Z71 Suburban, and 2014 Cherokee Trailhawk, but I'm not a mechanic. Just poor and stubborn!

Steve and his vast amounts of odd information never ceases to amaze me. Nice work Steve! At least I was right that it was an aftermarket (albeit dealer installed) system and remote. Anyhow, I defer to Steve on this subject, as he clearly has the experience with this setup.

Kudos to both of you! It all makes sense now. And explains why the GM part number on the back of the fob isn't matching the pictured front of that piece on eBay or wherever that exact GM part number showed a photo.
Thanks again!

After dealing with a few hundred of these things installed by the "professionals and dealers" in this area I will withhold my full opinion on them, suffice it to say that it is somewhat lower than a snakes belly.

As for finding the who behind may of the systems the FCC ID on the outside will usually get you better information that the part numbers. If you open the remote up like you are changing the battery there are many that have the makers information on the circuit boards as well.
Your FCC id starts with EZS which is a DEI code, Then the OEM which says it's a dealer installed item built for a particular company. The part number tells you the OEM in this case is GM.
There are a few companies that do these for the OEMs. The question then becomes "Was the guy installing them any good?" In this I have seen everything from a quality install where the wires were trimmed and soldered with self seal shrink tubing and the unit installed on a bracket with proper materials. Others were full length wires with connections made with scotch locks and zip tied in place and the lowest forms had the wires just twisted together and taped with the units just stuffed up under the dash behind the harnesses and just hanging there.

Same things happen these days. One of the first things I look for on security or no starts is an after market remote start or alarm. Most have no real testing options so you look at the wiring and what it connects to and try to bypass them as needed.

I've had similar experiences with a big tire chain's local retail store, and a big internet/phone only tire chain.
Poor feedback and application information despite detailed questions from me, poor quality tpms parts, terrible balancing job, wheel lock adapter left under the wiper arm outside, inability to properly register the tpms units fully. so now I go to the more expensive guys, just one visit.
You're connection with the force is strong Obi-Wan.
Continue to support us lower level gas pilots!

You're welcome. We will be here if you have any other automotive questions.

If you two guys are ever going to be out near Natural Bridge St Park in Ky, yell at me. I'll dole out some homemade chili and a cold beverage in appreciation of the help! We're near there often, usually twice monthly.
Pictured is the back yard. Name that wall, and I'll be totally awed. It is listed in several publications. The photo is from 1/6/19, the guy in white is about 300' up.