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Hi I just purchased a 99 Deville with 76000 miles today when I went to start the car I unlocked with key and there was no display on dash when I started the car the security horn kept beeping constantly. I tried to use the door lock button, but it wouldn't work. I also tried to unlock and lock the driver and passenger door again using the key. I do not have a key fob for this vehicle. 

I put the car in gear and the horn stopped? I drove it around the block and parked it shut off the ignition power alarm horn started going off again? I got out of the car put the key in the  door to lock and it stopped? Any ideas? The security light doesn't flash when I get it to start and the power door button seems to be disabled unless the power is on and car is started? 

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Hi

:welcomesmiley:

Dave,

The security system did not see the unlock command from the drivers door module when you unlocked it with the key. Since it didn't see the unlock command it initiated theft prevention, but it recognized the key and allowed it to start. When you put the vehicle in gear it cancelled the alarm.

After you stopped the vehicle the security system restarted the sequence. Once you removed the key and locked the door the security system saw the door lock command and reset the alarm.

Does your Deville have a key slot on the passenger door? ( I don't think my 99 Deville did ) When you stopped the vehicle after the drive around the block were the door locks locked? When you drive the vehicle over 7mph do the doors auto-lock? Did the door locks unlock when you put the vehicle into Park? Do you have to unlock the doors from the inside?

My thought is that the drivers door module is defective BUT don't rush out to the junk yard YET to buy one. If you can be a little more precise on the sequence of events, it makes a BIG difference what happens when. The alarm should have sounded as soon as you opened the door so I'm a little confused by what you wrote.

THERE IS ALWAYS ENOUGH TIME TO DO THE JOB RIGHT - THERE IS NEVER ENOUGH TIME TO DO THE JOB AGAIN !!!

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How is the battery?

Have you checked for codes?  

See my signiture here for the procedure to check for codes

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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I dont believe the 99 had door modules yet.

I believe it started in 2000 with the new body style for the deville.

I would suggest unhooking the battery terminals and touch the cables together, then try it again. Keep us posted.

Unlocking either front door with the key should turn on the domelamps (only if it is not light out)

2 turns should unlock rest of doors. (this is key. If this is not occuring then there is likely a issue to the cylinder) there is a sensor at the back of the cylinder

GM FAN FOREVER

Nice, clean, luxury= fine automobile

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26 minutes ago, rockfangd said:

 

I dont believe the 99 had door modules yet.

I believe it started in 2000 with the new body style for the deville.

 

That could be but the security system should disarm from the drivers door being unlocked with the key. The security system is not seeing the key un lock the door, the OP's description of the problem is not detailed enough to provide an accurate diagnosis at this time regardless if there is a door module or not.

THERE IS ALWAYS ENOUGH TIME TO DO THE JOB RIGHT - THERE IS NEVER ENOUGH TIME TO DO THE JOB AGAIN !!!

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Hello people! And thanks for the replies so far. This is a key only (no fob) I tried to unlock both doors with the key,  it it seems no light went on (it was daylight) idid notice the security light was NOT on at all on the display when I got in, and the power door locks would not work to lock or unlock unless the ignition was on and horn blaring. 

when i went around the block I didn't notice if the doors locked automatically but as I said when I put it in gear the horn stopped, and when I shut it down it started again. When I got out of the car and put the key in the drivers door and locked it the alarm went off. I didn't try it again but was going to go to the mechanics on Monday just wondering if I would be safe to drive it about 20 miles? 

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Hey thanks for that fast reply! Yes it seem to be fine driving. I was going to go out there anyway to have the coolant fill tank Checked out since it seems to run a bit hotter than I am comfortable with. And as I was reading about the notorious overheating on these cars and saw a lot of the problems can stem from a clogged coolant tank which would be great if that was it because it is probably the cheapest repair route anyway sounds good I'll let you all know what Monday brings!

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your domelamps will not come on during the day.

You say the security light does not flash on the dash when the key is off?

That tells me it likely has a aftermarket keyless entry and possibly remote start. that would also explain why unlocking the door with the key trips the alarm.

Look for a antenna somewhere toward the top of the windshield or by the rearview mirror. (not the rainsense module)if equipped)

If it does have aftermarket without a fob it will just keep tripping

GM FAN FOREVER

Nice, clean, luxury= fine automobile

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Okay so went to the mechanic, and of course the car started fine today no alarms ringing, etc.. he says it looks as though someone have already bypassed the VATS system since the keys don't have any raised chip on them, and he hooked up his OBD TOOL the keys were reading the unlock mechanism  on both doors so he suggested getting a key fob and having a dealer program it so this wouldn't happen again. Worth it I think not to go through the aggravation!

also had him remove the coolant tank to see if it was clogged, it wasn't  seems to be running a bit hotter than I like, but he said no worries when it gets warmer I will see if we need to address that further 

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did you do what I mentioned about the battery?

Go on ebay and you can get the set of fobs for not too much money. I dont remember if thee 99 can be programmed by the onboard diagnostic in the IPC or if it needs a scantool to be programmed. 

GM FAN FOREVER

Nice, clean, luxury= fine automobile

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Since the VATS is by-passed the mechanic gave you the best option. As rockfangd stated ebay is the least expensive way to go to get key fobs.

If the Tech2 is seeing the doors unlock I'm afraid if you do a battery disconnect the security light will come back on and you'll be back to the alarm sounding.

Of course the BEST method is to put the VATS back to factory "operating as designed" !!!! That could get very expensive BUT the vehicle is "pants down" ready to be "violated" at the moment. :blush::blush:  :wipetears

1997 was the last year for key fob programming through the IPC :(

Edited by OldCadTech

THERE IS ALWAYS ENOUGH TIME TO DO THE JOB RIGHT - THERE IS NEVER ENOUGH TIME TO DO THE JOB AGAIN !!!

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I wont go as far to get the vats back to factory, I mean the car is 18 years old, it's not like the Honda crowd is out wanting to steal it by any means!? But yes eBay is the cheapest I have found, and if a dealer can program those fobs then I will bite the bullet to have one and make life easier for sure.

appreciate all the fast replies and help here! 

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