E39 Car alarm going off randomly?

Does anyone have any ideas to what is causing the problem and maybe a solution to fix it.?

Its your interior sensor, buy a new one and your done.

Before making any assumptions and shelling out $$ on an interior sensor, try disabling the under-hood sensor. It's a hugely common problem on E39s.

Lots of discussion on it here:

Hood Sensor / Alarm issue

Try pulling the plug. See if the alarm still goes off randomly. This doesn't affect your main door/interior alarm sensors in any way.

Check the hood sensor. I had the same problem before, as soon as i replaced the hood sensor it stopped.

http://www.bimmerfest.com/forums/sho...errerid=119266

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.

1BAD540

You know you signature picture...the way your car is positioned with the driveway in the background...makes it look like you have a huge ricer spoiler on your car.

Originally Posted by cagoguy

Before making any assumptions and shelling out $$ on an interior sensor, try disabling the under-hood sensor. It's a hugely common problem on E39s.

Lots of discussion on it here:

Hood Sensor / Alarm issue

Try pulling the plug. See if the alarm still goes off randomly. This doesn't affect your main door/interior alarm sensors in any way.

Originally Posted by osikani

Check the hood sensor. I had the same problem before, as soon as i replaced the hood sensor it stopped.

http://www.bimmerfest.com/forums/sho...errerid=119266

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.

100% It's the hood sensor. Same problem, just disconnected it.

same prob here but on a E38.. Q, do you have a pic of the e38's hood sensor? from what i gathered, i disconnected a wire going from the top right bay into the hood. (driver side)

Originally Posted by Dking078

same prob here but on a E38.. Q, do you have a pic of the e38's hood sensor? from what i gathered, i disconnected a wire going from the top right bay into the hood. (driver side)

The e38 hood alarm switch is up by the expansion tank for the radiator...if that's not what you unplugged...I'd plug it back in.

Hood sensor, as mentioned. If that doesn't do it, check your battery.

Originally Posted by QSilver7

The e38 hood alarm switch is up by the expansion tank for the radiator...if that's not what you unplugged...I'd plug it back in.

thanks i should get right on it!

Check your battery voltage too; the alarm is designed to go off if it detects that there's a variance in the battery current in order to prevent battery tampering.

Hey all - Having the same problem... Replaced the battery...

I don't have the switch like Dking078 on my 97 528i - but I did unplug the one I have like QSilver7 and the alarm still went off randomly shortly after. Is there another hood sensor i should look for? or is that difference in years?

Otherwise can I disconnect the interior and be done with it?

Originally Posted by MadBMW

Hey all - Having the same problem... Replaced the battery...

I don't have the switch like Dking078 on my 97 528i - but I did unplug the one I have like QSilver7 and the alarm still went off randomly shortly after. Is there another hood sensor i should look for? or is that difference in years?

Otherwise can I disconnect the interior and be done with it?

What battery did you replace? The car's battery (in the trunk) or the key's battery?

+1 battery replacement. ( car battery) My alarm would randomly sound. The battery was wearing down due to an alternator that needed replacement. I replaced alternator and battery and no more false alarms.

+1 Hood sensor, had it replaced on current and previous E39 models with same problem. Have never replaced battery but should have it checked...couldnt hurt

My alarm was driving me crazy one night a few weeks back. Apparently a cicada entered into the car through the cracked sunroof and the interior poxy sensor set off the alarm every hour or so from the damn bug flying around. All is well now though I know if you double press lock it disables the proxy sensor...not sure if it does anything else

Do you mean the microphone?
Is there an easily accessible connector to disable this? My dogs will trip it when left in the car the moment they bark.

Originally Posted by QSilver7

What battery did you replace? The car's battery (in the trunk) or the key's battery?

Replaced the car battery... The remote is usually out of range so I doubt that would be the cause.

Seems like it goes off regularly after the car is parked for 30-60 minutes. Sometimes a few times mid day. Heat?

I disabled the hood sensor and still had the same issues.

Originally Posted by ross1

Do you mean the microphone?
Is there an easily accessible connector to disable this? My dogs will trip it when left in the car the moment they bark.

No, not the microphone... There is a motion sensor in the car. I bet Q has a picture of it lol... But to disable it just press the lock button on your key twice. (Press.... 1 second pause.... Press again)

AHHHH It still goes off every few hours during the day, sometimes back to back...

Where is this motion sensor? I want to make sure its bug free

Cant we unplug it?

The motion sensor is located in the traditional interior light position in between the driver and passenger on the ceiling behind the sunroof.

I tried to post this info about 1/1/2 hours ago but the forum wouldn't take it....

Originally Posted by ross1

Do you mean the microphone?
Is there an easily accessible connector to disable this? My dogs will trip it when left in the car the moment they bark.

Originally Posted by CoreyMNK

No, not the microphone... There is a motion sensor in the car. I bet Q has a picture of it lol... But to disable it just press the lock button on your key twice. (Press.... 1 second pause.... Press again)

Originally Posted by MadBMW

AHHHH It still goes off every few hours during the day, sometimes back to back...

Where is this motion sensor? I want to make sure its bug free

Cant we unplug it?

The IMS (interior motion sensor) is located under the the small thingy in the center of the roof liner. And as you can see in the image below from the owners manual...it states NOT to leave pets or small children (adults, too) in the car when you've locked it with the key!

Images below are from farnarkler's DIY write-up on www.e38.org on how to upgrade from the old RF (radio frequency) IMS...to the newer (ultrasonic) IMS.

This is the older IMS (it's an RF sensor):

...and this is the newer style IMS (it's an ultrasonic sensor)...and has the grid/slats in the cover:

i once had a problem like this...hehe.. it turned out i left my cellphone in the car... and people were rining me... i would goto the car.. disable and re-arm the alarm...
true as bob later on it would randomly go off again... only LAAATER when i was looking for my phone did i click what had happened.,
like 8 missed calls on my cell. around the same amount of times the bloody alarm went off...lol