Hey fellas. I've got a '99 TL with 100K miles. In the last few weeks, the security system has been acting up. I've searched the forums and have done a bunch of troubleshooting on my own but still can't figure this thing out. Of course, I'm hoping to avoid the dealer.

The alarm started going off on its own and did this for a week. Eventually, I was blowing fuse #5 for brake lights and horn. I concluded that it was going off so much when it was parked in the lot at work that it fried the security horn (on the strut tower). I disconnected that and it stopped blowing the
fuse.

The security system would not set when locking the car (no flashing lights, blinking LED).

I checked the door switch sensors, pulled the hood latch where there's a sensor, all wiring is OK.

I disconnected the battery and it reset the security system. The lights blinked and worked as designed with the remotes for about 1 day. Then the problem comes back and system works intermittently (only 1/15 times) . It will reset and work every time I pull the battery.

I also noticed that when I reconnect the negative battery terminal it arcs and I get sparks (I never remember this in the past.)

I've read there is a sensor in the trunk latch and you can have alarm problems if this is bad. Is there any way to test the trunk latch? The trunk still opens with the remote and the switch on the driver's door.

Any ideas?

 

I forgot to add, I replaced the batteries in the remotes and that didn't change anything.

 

Bump. Posted a week ago. Nobody has any ideas?

 

Free bump - My 2000 TL alarm just started randomly going off tonight. Any ideas from anyone?

 

Bump - Anybody???

 

Could the security system be messed up by a faulty ignition switch? Is so, you might want to just go ahead and replace that. It's a $50 part and my 1999 TL is already on its third switch. (The first one was replaced under the recall.)

And Helminc.com does sell an electrical troubleshooting manual for the TL. Maybe that would be a good investment at this point.

Good luck,

Bob

 

My guess is one of the switches on the doors, trunk, or hood is not making good contact when they are closed (or is making contact when it shouldn't be; I don't know if the switch should be open or closed when the door is closed). That's why it won't arm sometimes, and when it does, it'll go off when it intermittently.
Check all of the sensor switches, or next time you get it to arm, wiggle the doors, trunk, and hood one at a time until the alarm goes off, then you've found the offending switch.

 

This was a tricky one to diagnose and fix. The solution in my case was replacing the hood latch.

If the security system is not functioning or the horn and lights are going off haywire, the problem is with one of the sensors. On these cars, there are 6: one in each door jamb, plus the trunk latch and the hood latch.

See if your hood latch is flaky by trying this: Unlatch hood and lock doors with remote. The security system should not set. Without latching the hood, slowing push hood down like you are going to latch it (there's maybe an inch of play there). As you're slowing pushing, keep pressing the lock button on your remote. If horn beeps and lights flash, alarm is set. On my car, the alarm would set somewhere between open and fully latched and closed.

Working intermittently is the biggest problem because the alarm could go off in the middle of the night, while you're at work, etc... Mine was so bad that it fried the security horn and drained the battery. It can also blow your brake light fuse (lights flashing all the time overload the circuit) and when it does this your shift lever locks up and you won't be able to get the car out of park.

If you can get the security system to set when messing with the hood position, your latch is junk-- order a new one.

To disable security system: Remove plastic trim panel than runs the width of the front end to gain access to the hood latch. Remove 3 bolts holding hood latch and mark position of latch. Follow the wire harness and disconnect the electrical connection to the latch (gray plug). On female end of plug, insert a piece of wire and short the one pin to the other. This will cut the alarm circuit. Reassemble hood latch. You'll still be able to lock and unlock doors as normal but security system will be disabled.

When you get the new hood latch, pull the jumper wire, connect new latch, reassemble and magic! Everything should work again.

 

I have some what similar problem. ONLY my alarm sets, but horn does not sound when I lock the car. I know slowboat said it might be hood latch. But it use to work just fine, until I had to replace the whole door on my passangers side.
Any suggestions????

 

Since there was bodywork done on your car, I'd suspect the sensor in the door jamb where the door was replaced could not be working. Was the door replaced because of an impact? If so, it could have been damaged. The switch is on the striker side of the door (black rubber boot held on with a screw, about the size of your thumbprint). This part is cheap.

FYI, if you hit the lock button twice on the remote, the security system is functioning normal when: 1. Lights flash. 2. Horn beeps. 3. The red LED at driver's door lock button flashes. If your car does not do this, a sensor/switch is out of adjustment or faulty and the car thinks a door is open.

If your lights flash and horn does not beep, problem is with security horn mounted on left shock tower. It is a different horn than when honking your horn!

 

slowboat- I have a similar problem, when you lock the car via remote, the lights flash and horn sounds, but there's no LED on the driver's door? Bad LED???

I forgot to mention that it seems to work fine in Panic mode so I'm assuming the alarm system's ok? Any help would be great!

 

I've never heard of that little LED by the door lock button going bad, but anything is possible. If you lock your with the remote and the lights flash and the horn beeps, this indicates that the system is operating correctly and the alarm is set. The LED should also blink.

I'm pretty sure you can test the security system operation by leaving one of the windows down and locking the car. Simply unlock the door with the button and open the door and the horn should go crazy.

If everything checks out, you may have a bad LED. However, keep and eye on things. My security system started acting goofy only once every week or two. Then the problems increased in frequency.

 

k thanks!

 

i have the same problem. My alarm keeps going off too.
I know my hood sensor is probably messed up because i can set the alarm and lock the doors with the hood up.

I can also lock the doors and set the alarm with the trunk open, is that normal?

 

my alarm doesn't go off the security light doesn't blink and when i press the lock button on my remote twice or more the lights do flash and give me the beep sound any ideas

 

I'm having a problem where about one in three times that I open the trunk the alarm will go off, though this doesn't happen until I physically lift the lid up. I would assume this is a bad latch or something like that, correct? The shop that installed my spoiler would likely be the source, they were ripping the lining and everything out of the trunk lid with some force. How much would this be to fix?

 

Properly functioning security system= All 4 doors + hood + trunk closed you will be able to lock the doors with remote and lights will flash. Red LED at door lock button will blink. Double-click lock on remote and horn will also beep.

If upon locking your lights flash and horn beeps BUT LED at door lock does not blink, there is a fault with the LED.

You should not be able to lock the doors with the remote if the trunk is open.

You can lock the car with the remote if the hood is open but security system should not set (lights won't blink, horn won't beep, no LED).

If the alarm sounds when opening the trunk, the trunk latch is either bad, has faulty wiring, or is out of adjustment. If you didn't have this problem before the shop installed the spoiler, take it back to them. They should stand good on the install and fix the problem.

 

I can confirm that I had the exact issue and the culprit was the hood latch alarm sensor.

Until last night, I was simply unable to arm my system (no lights/horn beep) but able to lock everything. I didn't know what was up, and then last night the alarm started going off randomly, 1am!, every few minutes. Finally I just left it unlocked.

I perused the forums with my new found 'random alarm going off' as a search string and ended up here. I tried popping the hood, and sure enough, the alarm armed just fine with it popped (not fully open, just unlocked from inside). This confirms a faulty, in one way or another, hood latch/sensor.

Right now, I am just booting around with the hood 'popped', still secured via the little release lever, but popped from inside the car. The alarm arms and beeps/flashes, and no longer goes off randomly....for now!

I'm going to investigate the hood sensor/latch now, to see if it's loose or what my options are. Anyone know where this is located?

I searched some more and found a few threads that supposedly had diagrams referenced by posters, but they were old threads and the images were gone.

 

The alarm sensor is an integrated part of the hood latch.

Remove plastic trim panel than runs the width of the front end to gain access to the hood latch. Remove 3 bolts holding hood latch and mark position of latch. Follow the wire harness and disconnect the electrical connection to the latch (gray plug).

New latch ordered from dealer or a discount supplier has the electrical connection. Connect your wires, bolt in your new latch, and close the hood. Test security system operation and adjustment of hood latch. If everything works, put back black plastic trim panel and have yourself a beer.

Chris