So today I get home from running an errand. Go back to the car open the unlocked door and the alarm goes off. I didn’t even know it had one. Put the key in turn it and it shuts off. Leave it unlocked. Go insider a few hours later remember to get something from the car, open the door and the alarm goes off again. It’s not even locked when this happens. How do I shut off the alarm or better yet disconnect it all together?

1996 LT4. I don’t have a key fob.

 

When you turn the key to the ‘on’ position, does the “Passive Keyless Entry” light come on in the DIC? If it does, unfortunately you’d need a keyfob to turn it off. But it shouldn’t arm unless a keyfob synchronized with the car has been in range prior to the driver’s door shutting.

Does the SECURITY light flash when you open the driver’s door? Or is it on solid?

 

I have had the car running and driving for a while now, couple of months and this has just happened today. I have never had a keyfob so I am not sure how it could synchronize with a keyfob.

I will check and get you answers to your questions tomorrow.

Thank you
Doug

 

There is a rare condition, in otherwords don't start here first, but with the doors locked and security engaged the CCM monitors electrical draw in the car. There can be a very slight variance in the steering wheel contact for the horn, if electrical power goes through there, doesn;t take enough to blow the horn but it is enough to tell the ccm someone is in my locked car trying to blow the horn - alarm goes off.

 

Indeed. The odd thing is that the alarm system is arming at all.

Per design, it should only arm if the PKE system is engaged, and a transmitter was within range before the driver's door was closed, then went out of range. This will then lock the doors, beep the horn, and arm the security system.

With the PKE system disabled, pressing the power door lock switch to the 'lock' position before closing the driver's door will do the same. Lock the doors, arm the security system.

The difference is OP says he has no transmitter, and has not touched the power door lock switch. Yet the CCM appears to be arming the security system anyway.

That's why I'm curious as to whether the PKE light comes on in the DIC when the ignition switch is turned to 'run', and whether the SECURITY light is flashing when the driver's door is opened and closed.

 

I suspect we don't have all the information

 

It might be a long shot, but thoroughly search the car for a fob hidden somewhere. Look in the arm rests, center console, under the seats, etc.

 

I had my 96 lock me out while I was at a friend's house working on the car. The keys with the phob attached were in the ignition. I had opened the doors a few times no trouble. I opened the passenger door and closed it and the system armed itself and locked me out. Its not suppose to do that with the phob inside or close to the car but it did.

 

What some people are missing here is that the car isn't locked. OP says the car is unlocked and he's opening the unlocked door. So OP is definitely describing a faulty condition of the CCM's alarm operation, and it's important that we start to collect clues to tell where in that system of circuits the fault may lie.

 

So , have the door panels ever been off? Has the car been painted? Before I decided that the CCM has reprogrammed itself, I would eyeball the security light EVERY time I get out of the car and before I open the door, keep doing it, no fudging, and see what the light is doing. Then I would take the doors apart and see id the lock cylinder arming switched (that are NLA) are damaged or not installed correctly or worn, the are insulated and go in a certain way in the tumbler, if they are installed wrong, plastic insulation worn it can arm the system, heck if you don't have a fob remove the arming switched from both doors.

 

You're right, nothing to do with fobs, my bad.

 

While I'm inclined to agree, it still begs the question of why when the CCM receives the UTD-enable command the horn does not beep and the doors do not lock.

 

Because it isn;t being armed by PKE removal. That is why I have my input to the lock sensors in the door handles. They arm without the confirmation chirp.

 

Update:

I didnt get to mess with this until today as it has been raining here.

Today I went out and opened the unlocked drivers side and nothing happened. Security light was blinking. Put the key in the ignition and turn it to the on position and there are no lights on the DIC about the security. And the security light is off.

Take the key out close the drivers door and go to the passenger side and open that unlocked door and the alarm goes off. Turn the key in the lock and the alarm stops.

I have since then opened both doors and driven the car around and it hasnt happened again... Very weird.

I will try to repeat it again later and see if I can figure out how I am arming it.

There is alot of good info on this thread. Thank you.

 

Pretty much this. We now know that the PKE system is not active, since there's no "PASSIVE KEYLESS ENTRY" light displayed on the DIC. If the PKE system is not active, then a rogue programmer somewhere in the car isn't the culprit, and this also explains why there's no horn beep when the system arms (it's not arming via a signal from a PKE transmitter). But as IHBD says, the PKE system is still the "core" of the alarm system, and is what tells the CCM whether to arm it or not. Additionally the PKE module is what's controlling the door lock motors, and telling the CCM whether the doors are locked or not (well, specifically, whether any door is locked and when the driver's door is unlocked).

So here's the issue.

The PKE system accepts an input signal from the power door lock switch. When this switch is pushed to the 'lock' position while the driver's door is open, it arms the security system (you can tell because the SECURITY light will stop flashing and go solid). The PKE controller then activates both door lock relays, and the door lock motor output voltage tells the CCM the doors are locked. What's most odd here is that you appear to be having the system arm despite no actuation whatsoever on the door locks, even though a signal from the power door lock switch should absolutely result in the door locks cycling.

Do your power door lock switches work, OP? Can you lock and unlock the doors with them?

If the power door lock switches do work, and the locks do both cycle, then I'm leaning towards a faulty PKE unit or an intermittent short to ground on the 'ARM UTD' line to the CCM.

If the power door lock switches do nothing, then it opens up a can of worms since the problem could be faulty door lock relays, a faulty PKE module, faulty door lock motors...bunch of stuff, and likely not only one problem.

 

The power door lock switches do work.

 

I did recently replace the drivers side door ajar switch. The old one would not turn off. I did notice the new one I installed was stuck on the depressed position yesterday making the car think the door was closed when it was actually open. I am not sure this would have anything to do with it. I tapped it and it popped out like it should.

 

I don't think the door ajar switches have anything to do with it. Your alarm goes off when you open a door, which seems to indicate they're working.

Since the power door switches do work, I'd expect a short to ground on the ARM UTD wire between the PKE module and the CCM. At this point you'll probably want a Factory Service Manual if you don't have one already.

That said, here's one of the pages for ya:




That wire is normally 12V. When the PKE module sends a request to the CCM to arm the system, it drops down to between 0.5V and 1.0V. If it's shorted to ground intermittently, then it's randomly telling the CCM to arm the system even though there's no other inputs.

 

I can't confirm your version of how the UTD signal works because the FSM doesn't describe the action of the UTD arm line during power door lock actuation. However, I can confirm that your description of how the power door lock switches work is incorrect. Please see the below excerpt from the FSM:



As you can see, the only connection to the power door lock switches is the PKE module. And the only connection to the door lock motor relays is the PKE module. Thus, the PKE module is what's controlling the power door lock motors in response to a signal from the power door lock switches.

If your description of the UTD arming procedures is correct, however, then indeed a voltage leak on the CCM Lock Input wire somewhere would be a likely culprit. As always, thank you for the additional clarification.

 

Figured out the problem. Removing the PKE fuse doesn't actually shut down the PKE system. You have to remove the PKE fuse as well as the RDO fuse (fuses 26 and 40). With both fuses removed, the PKE system no longer responds, but as expected the door lock switches continue to function, and the CCM continues to arm the UTD system.

As always, it's excellent to have such detailed information available to the community through your posts. It's really too bad the diagrams in the FSM didn't show the internal connection between the door lock switches and the door lock relays!

EDIT: For OP, this changes my opinion; it would appear there's voltage leaking on the "Lock Input" wire to the CCM (in the above diagram I posted, that's C4, the grey wire). If voltage is on that line, the CCM is going to assume the door lock motor has actuated, and it's being asked to arm the UTD.