E39 Car alarm going off randomly?

I had the problem of the alarm going off when I was parked on a slight downward slope, and passing traffic would generate enough road vibration to set off the motion detector. Once that was disarmed, it was fine.

Also had the problem last week in the middle of the night as my battery was apparently going dead from an unknown/undetected drain. Finally had to leave it unlocked in my driveway for a few hours until I got up and recharged the battery.

+1 on the cell phone bit!!! I have a blackberry and left it in my 540, it didn't just set the alarm off when it rang, but even when it was searching. I'm wondering if maybe the infared is setting it off. by the way, just to make sure, i placed my daughters regular phone in it and it did nothing.

+ 1 Million on the Hood Sensor. Even my X5 is yappin in the middle of the night. Probably the damn sensor!

so i have been having the same problem mentioned a few times in this post.. i took out the fuse by the battery.. and now the alarm obviously doesnt go off but when i lock the car.. after a few minutes.. the lights start flashing as the alarm going off except the sound.. any suggestions?

Disconnecting the hood sensor worked for my 2002 525iT. For the first time in months I don't have to open the back door in order to lock the front door.

me too... hood sensor... unplugged... issue solved.

I had my truck open on its own once and set the alarm off. It just went off again last night in the garage (only the second time ever), and while I played with the trunk before leaving for work I don't know for sure if that was it this time. Hood sensor, hmm...

http://www.bimmerfest.com/forums/sho...5&postcount=61

What do we look at next when it is not the hood sensor

Just went to unlock my dad's '04 X5 in Walmart's parking lot, and... BEE-EEE-EEE-EEE-EEE-EEE! Yeesh. :/

Originally Posted by 87vert

http://www.bimmerfest.com/forums/sho...5&postcount=61

What do we look at next when it is not the hood sensor

disconnected hood sensor, disconnected sensor in roof. Double tap lock key. Replaced car battery.

Alarm goes off after about 5-10 mintues.

Any ideas? Alarm module?

I am reviving this thread because I see it died right where it got interesting for me. I noticed no one answered the last question in this post. I have a 2000 528IT, 86,000M, and have had an alarm problem for 6 months or so. I have taken the battery out and had it bench tested, I have disconnected both the hood and interior roof sensor and the stupid thing stills goes off even if I try the double lock thing.

I can count on every second weekend going out to the car to find the battery completely dead and having to charge it overnight...why? Because the siren goes off, then shuts off, but the lights sit there and flash causing a drain on the battery; the lower the battery gets the more this stupid car thinks its being tampered with and sets off the alarm again, thus draining the battery some more, which in turn sets off the alarm again (see the pattern?)

Is there any help out there to solve this problem? I have read about rechargeable batteries being inside the alarm somewhere that wear down after time. Is there something I'm missing or do I have the one off problem to which there is no fix...

Chck out a treand in the E38 side. Theres a newer post about draining battery. It has'nt really gone anywhere yet, but keep an eye on it. Sorry I cant be of more help.

Belicek,

I can't comprehend that you have not taken this to a mechanic to get fixed.
You really let this insanity go on for SIX months?????

For others, here is a review of possible things to try:

• Check if the battery is loose.
• Replace the battery with a new one.
• Detach hood sensor.
• Check door latches/sensors
• Disable motion sensor by press key locking button twice
• Detach inside motion sensor
• Unplug fuse #48 in trunk

Beli tried the hood sensor, would have been good to test a brand new battery. Try opening the 'secret menu' and checking alternator voltage just to be sure it is getting good charge while you drive.

Lots of people say it's the hood sensor, but what is it about the hood sensor?
Can it be repaired? Is it shorting out (i.e. going open position when closed)?

Originally Posted by hqstu

...what is it about the hood sensor?
Can it be repaired? Is it shorting out (i.e. going open position when closed)?

It's so inexpensive, it is probably easier to replace...or like many owners...the threat of someone tampering with the hood is so minuscule, they just UNPLUG the electrical connector from the hood sensor:

1. Note how much dirt/grime/dust collects on the hood sensor switch...this could cause the pin to stick or not fully retract or expand.
2. Take note of where the sensor is located...if the micro-filter housing has been opened/closed to replace a filter...it may not be aligned properly or the plastic clip that secures the sensor to the housing may have cracked slightly.
3. You may also want to notice where the "tip" of the pin contacts the hood. You may think that it contacts the metal section of the hood...when in fact, it may be pressing into the insulation on the hood...if it is...check to see if that area is worn away...or has been pushed up by the pin and no longer compressing the tip of the pin down far enough.

If you have some type of powder, chalk paint or fingernail polish...you can slather the top of the senor's pin, then close the hood...this will mark where the tip of the pin contacts the hood. If this contact point is the insulation versus the metal part of the hood...worn insulation may be the cause of the sensor not making proper contact.

Originally Posted by EconoBox

Belicek,

I can't comprehend that you have not taken this to a mechanic to get fixed.
You really let this insanity go on for SIX months?????

For others, here is a review of possible things to try:

• Check if the battery is loose.
• Replace the battery with a new one.
• Detach hood sensor.
• Check door latches/sensors
• Disable motion sensor by press key locking button twice
• Detach inside motion sensor
• Unplug fuse #48 in trunk

Not all of us live next door/near a BMW dealer, that's why. The nearest stealership is an hour away and of course the maintenance department is closed during the weekend requiring me to take off work. Then, I get the joy of bending over while they shaft me for hundreds of $$ to change a part that my son could change in 5 minutes. (Not a big fan of dealerships if you couldn't tell). I called one up the other day concerning this issue and was told that my car was too old; they usually don't deal with cars of this age. 12 years old with 86,000 miles...nice customer support...makes me want to race out and buy another one.

This is my second BMW, the first I had while assigned in England; it was a 535, got 38 MPG, and parts could be attained anywhere, relatively inexpensively. Fast forward to my return to the states where I buy another...talk about a different story. This one gets 19 MPG, weighs a lot more and parts are outrageously expensive...and that's for used parts. I contacted Barvarian for a used stereo part in the boot...$350 for a 12-year old stereo part.

But I digress...

As to your list...

Battery is less than one year old, passes all tests and is quite secure

Hood and interior sensor are disconnected (is there a tilt sensor somewhere? are there any other sensors to disconnect?)

No need to push button twice if sensor is disconnected, this takes it out of the picture. (Is this correct?)

Fuse 48 being unplugged does NOT disarm the security system; just the siren, lights will still flash if the alarm is activated.

Just this morning after I arrived at work I double locked the door with the key and 2 hours later the alarm went off again, the siren stopped but the lights flashed for an additional 5 minutes (yes, I timed them). I just charged the battery overnight (It was totally dead again after this last weekend of sitting in the driveway not being driven)

I am a mechanic and have my own private shop w/lift, I say this not to brag but to inform that I am not a total newbie when it comes to turning wrenches. I even built my own tool ($480.00 from BMW cost me $38 to build) and changed out the rear suspension bushings myself. This problem has me quite perplexed. What I am finding strange is the lack of anyone else having experienced the same thing before. Usually forums, if searched long enough, will reveal someone who found a fix.

I think the next step is to put this POS up on the lift and gut the alarm in the wheel well; my concern is that it will disable the car but what good is a car that won't start because the alarm keeps draining the battery? I have read that there are rechargeable batteries that are in the siren portion of the alarm system that die over time (great design!) causing the system to repeatedly activate...I will focus on that area for now and report back what I find.

If anyone has additional information that I missed or have wrong, please let me know. The depreciation on these cars is so bad that I am basically stuck with this thing so I have to figure it out. I should have bought a Toyota!

I'm not sure if you've fixed it yet but I will +1 that its the hood sensor. I had the same issue on my car. I thought it just wasn't mounted well so I ziptied it better and it still went off. Got a new hood sensor and the alarm hasn't went off since.

Originally Posted by midnitemyst

I'm not sure if you've fixed it yet but I will +1 that its the hood sensor. I had the same issue on my car. I thought it just wasn't mounted well so I ziptied it better and it still went off. Got a new hood sensor and the alarm hasn't went off since.

One quick way to rule out the hood sensor is to disconnect it. If the alarm stops going off then that was the problem. If not, then keep looking.

One of the first things I tried was the hood sensor; it has been unplugged for months so it can't be the culprit of setting off the alarm.

See also:
- How to understand the BMW E39 EWS alarm drive-away protection system (1) (2) (pdf) & troubleshoot the alarm & hood switch (1) (2) (3) (4) or replace the siren (1) or disabling or enabling the unlock chirp (1) (2) (3) & how to maintain (1) and repair your hood release bowden cable (1) (2) (3)

Originally Posted by bluebee

See also:
- How to understand the BMW E39 EWS alarm drive-away protection system (1) (2) (pdf) & troubleshoot the alarm & hood switch (1) (2) (3) (4) or replace the siren (1) or disabling or enabling the unlock chirp (1) (2) (3) & how to maintain (1) and repair your hood release bowden cable (1) (2) (3)

Thank you for the reply. I have read many of the posts listed and am further intrigued to see a reference to the batteries in the siren again. On another BMW forum, there is someone who took apart the siren to get at the batteries within, while he did get inside, the siren had to be cut open, thus ruining it. I have a pretty hard head and don't like being told by a designer that something just has to be thrown away because of their pi55-poor design. I am going to put my POS on the lift and remove the siren then see if it will run without it. If so, I will start experimenting with a disassembly to get at the batteries. I'm sure Radio Shack can source the batteries. I am not going to pay $150 freaking dollars because some short-sighted engineer decided to put batteries in the car's permanently sealed siren.

As the old saying goes, necessity is the mother of all invention...

One final question regarding the sensors:

Are there any other sensors which can be disconnected on a 528it besides the hood and interior roof sensor?

Thank You

I placed the POS on the lift and removed the siren last night; took about ten minutes and it was in my hands. After I removed the three screws holding it together I found it was sealed at the seam as well, probably to insure a moisture barrier due to hostile environment where it's mounted. I took a razor knife and repeatedly scored the seam until I was able to get a portion to separate, be patient and gentle, like most things on this car, it is made of recycled brittle plastic and it will snap in a heartbeat.

After I separated the case, I found three batteries wired together in a triangle pattern to form a total of 6/250H 7.2v which plugs into the siren via a small two-wire harness. Of course I couldn't find the battery setup anywhere except European websites but I did find the individual batteries 2/250H 2.4v, with wiring tabs, on E-Bay for $7.99 (free shipping too); I ordered three of them and will solder them together myself. My belief is that I can remount these back into the siren, seal the case back up, hold it together with the original three screws and place it all back together in the wheel well. I see nothing prohibiting this from happening.

A savings of $140, a minor investment of time and the joy of doing something I have not found anyone else attempting yet.


On a side note, the car runs fine without the siren, the jury is still out on whether the lights will continue to flash because something else was the cause of the alarm going off. I will update when I have it back together.

Originally Posted by razzy530

+ 1 Million on the Hood Sensor. Even my X5 is yappin in the middle of the night. Probably the damn sensor!

Mine was rusty contacts on door switch, used contact cleaner & clicked it many times, solved it.

Originally Posted by JasonSC540ia

I had the same problem on my 97 540i. I disconnected the hood sensor by the driver side cabin filter and it stop doing it.

Did the same thing on mine. Quick 30 second fix and it still allows the keyless entry to work. I don't care about the alarm- I live in Iowa!

If my school police drives by my car it sets off my alarm! Something to do with the frequency they are on.