Alarm Going Off Randomly

[mgfranz]

So this is weird, I can let my '01 986 sit for a day or two with no issues, put a few miles on it, bring it home and park it and everything is fine. Go back out after a day and drive it for a few miles, park it, lock the car, and the alarm will just go off after 10 minutes.
I deactivate it with my FOB, check the vehicle and relock it. I can be standing near the car and the alarm will just go off by itself. What would cause the alarm to just go off? Could sensors be going bad? I know we can't disable them due to the immobilizer, and they can't be tested that I know of...

[Zzorro]

I'd be checking the CLU under the drivers seat for moisture damage. Whenever I have read about alarm issues, that's usually the 1st place people are instructed to look.

If there is any moisture, I would check the drain holes under your convertable top to make sure that they are clear and working properly. If those are plugged, you can get water right into the cabin.

My CLU is pooched. But car still starts, runs and drives luckily. I know I gotta get around to fixing it eventually. It's on my list.

Could be something else of course. But this is an easy check.

[Paul]

Have your alarm codes read. Could be any of the alarm points including the doors, trunks, motion sensor, radio, etc.

[mgfranz]

Originally Posted by Zzorro

I'd be checking the CLU under the drivers seat for moisture damage. Whenever I have read about alarm issues, that's usually the 1st place people are instructed to look.

If there is any moisture, I would check the drain holes under your convertable top to make sure that they are clear and working properly. If those are plugged, you can get water right into the cabin.

My CLU is pooched. But car still starts, runs and drives luckily. I know I gotta get around to fixing it eventually. It's on my list.

Could be something else of course. But this is an easy check.

I pulled the seat today to check for any moisture, dry as a bone. But I did pull the CLU and opened it up to check the solder contacts since I have seen solder joints fail before on my BMW's. After a close magnified inspection I found no bad joints so I did a good cleaning thinking maybe it might be just 20 years of grime. I'll put it back together tomorrow and let you know results. Might have just been a bad connection.
But either way, it gave me a chance to fix the seat recliner lever.
I'll check alarm codes tomorrow.

[mgfranz]

Just to follow up, no codes were thrown. However after a bit of troubleshooting and reading through several hundred threads with the same issue, I believe I found the issue.

Most of the troubleshooting came with watching the interior lamps after changing the 15 amp fuse on the CLU. When I replaced the fuse the lamps came back on immediately, which a good sign. But before I tested the locking system, I disconnected the alarm horn because in a number of posts others have said that the horn was shorted and would blow the fuse as soon as the FOB or doors were locked. After I disconnected the horn, I took a good look at the wiring of the CLU connectors and may have stumbled upon an issue. The "wire", if that is what it is, the single wire or fiber cable off the CLU may have been loose or not secure, so I used a piece of 3/16 heat shrink to secure the connection. Tested everything and for 3 days now I have not had an issue whether using the FOB or the key to lock.

I have to do some research to see how to test the horn, but I may just make a simple circuit with a fuse on a 12v loop to see if it was the fault. Anyone know what the resistance of the horn parameters are?