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Recently I've noticed my alarm will go off for no reason, randomly when the car has sat in the sun all day at work. Then this past week, when it is out in the sun, it always goes off when I hit the key fob unlock button coming back to the car. I.e. the alarm is armed, car is locked, sitting there normally, but hot. I hit the unlock button, and the alarm goes off.
I'm guessing there is some module that is getting old and a bit melty. Can anyone point me in the right direction?
Edit: I suppose I should have google'd, first result that comes up says check the battery voltage. I'll have a look at it today at lunch and report back.
Last edited by Aitch; 06-26-2017 at 10:57 AM.
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Try disconnecting the motion sensor on the roof. That's what I figured out on a customers 7. Hasn't gone off since
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I've wondered about that for the random alarm issues during the day. I know occasionally it has been set of by loud Navy jets/helicopter flyovers here at work in San Diego. But it may be faulty as well, or affected by the heat.Originally Posted by Sundaycruzer
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Check the hood switch as well. That was the cause of my similar issue.
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Are you leaving any windows or the sunroof cracked open? If so, this could be setting of the IMS (interior motion sensor) as previously suggested.
The IMS can easily be deactivated by pressing the LOCK button on your remote key TWICE...or turning the key manually in the driver's door lock cylinder TWICE. If you do this and the false triggering stops...then you've found your culprit.
{instructions to disable the TILT & IMS sensors}
Or, as the other suggestion (and common culprit)...you can raise your hood and disconnect the electrical harness to your hood alarm sensor (tie off/secure the connector so that it doesn't drop down into a difficult place to grab it in the future). If you disconnect the hood sensor...and the false triggering ceases...then again, you've found your culprit.
{e38 hood alarm switch location}
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Thanks Q.
Update: after sitting for 5 hours at work, the car's battery voltage measures 12.0V according to the cluster. Looks like that is in the low end of the charge performance chart (<25% charge).
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Further update. Measuring battery with a volt meter showed 12.08V after resting. While driving home the car displayed 13.6-13.9V so it's definitely getting charged. I also unplugged the hood sensor so I'll see if that makes any difference tomorrow.
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SitRep: replaced the car's battery yesterday. Getting a good ~12.3V at rest now. Alarm still went off this morning when I unlocked the car. Most likely culprit now is an undercharged/failing siren. I'll try disconnecting that and see if the alarm still triggers when I unlock the car.
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just had the same problem, replaced the hood switch.....hasn't gone off since...
try unplugging it for a few days first, if it doesn't go off then it was your hood switch.
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No, my hood switch has been unplugged since Monday to eliminate that as the problem.
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So is it still going off?
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Yep, came out and unlocked it this morning, alarm went off. The battery voltage was fine as expected.
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Have you disconnected the proximity sensor yet?
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No but as I mentioned in the other thread I will try that too. Thanks for the additional details.
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Move to a cold climate.
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I think I know what this is.... I went through the whole thing myself last year. it got worse when I took the battery out to charge it and it just became obvious that the low charge of the siren eventually went flat completely. If all the obvious things dont work, then its down to the siren itself. I went to pick n pull and picked out a late model siren so now my 98 sounds like a 2001. I call that a win! good luck with yours!
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Pulled the interior motion sensor. Alarm still went off this morning when I unlocked it, and actually took a few tries of locking/unlocking to get it to stop. Tomorrow I'm pulling the siren plug (haven't had the motivation to get the jack out yet to lift the car).
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I went through this a couple weeks ago. I just pulled fuse 56 above the battery. Alarm never goes off now but still get the flashing LED on the dash which might deter thieves. Don't pull fuse 58, it is the Central Locking System.
The fuses start with number 49 towards the front of the car. Here are the diagrams.
e38 trunk fuse index.JPGE38_Rear_Fuse_Diagram.gif
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Awesome, thanks for the reference.
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Wolf whistle?
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Yeah. I'll miss it if I can't get another lol.
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I've seen quite a few posts of the ye ole wolf whistle going bad. From what I understand it's the battery in the siren that fails starts leaking and then failure or your problem. At least now you are familiar with your alarm system, right
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Very, lol.
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I would have thought proximity sensor because of heat but siren battery issues seem to be trending lately. When you get it out take it apart, sometimes if it hasn't damaged the circuit board it could be repaired...if you care
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Finally removed the siren in the wheel well this weekend. Since then the car alarm does not trigger when unlocking the car. I will eventually replace the siren but for now at least I can lock the car without worrying about the siren going off each time I unlock it.
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