Alarm and Bonnet Switch Issues

[njathind]

Hi guys, having some issues with my Z3 randomly screaming its alarm off at silly hours...
Usually when I park it away from home, maybe its trying to tell me something...

Anyways I've tested the door switches and boot switch, all are working fine. I'm assuming that I don't have a roof switch as mine has a manual roof?

I've tried testing the bonnet switch and trying to trigger the alarm by locking the car, holding the plunger down, waiting for a minute then releasing the plunger but I cant get the alarm to sound. Could this be my issue? I've not had a chance to check if the radio switch is connected properly yet as its dark and wet outside.

I don't know if its related but my car randomly gives me a double indicator flash when I unlock it sometimes, not all the time but once in a blue moon. If the alarm has been triggered and I unlock the car I also get a double indicator flash.

Scratching my head here and its frustrating me that I cant solve it.
Many thanks in advance.

[Robert T]

A few things to point you in the right direction. I am assuming here that you have the later alarm with the buttons on the key rather than a separate fob.

Firstly the bonnet switch and radio anti-theft switch are wired in parallel. If the bonnet switch has no effect then the radio switch is already triggered. If you have an aftermarket stereo, then it likely hasn't been refitted. I cable-tied mine to simulate the radio being present. You will likely see your alarm LED flash rapidly after locking to indicate a sensor is in the tripped state - which the alarm should then go on to ignore. You want to fix this, as the alarm can potentially be disabled from under the bonnet.

The roof microswitch has nothing to do with the alarm. The protection against the roof being slashed to gain entry is the same as when the roof is down - ultrasonic sensors in the footwells. To test these for a fault you can disable them by pressing the lock button a second time within a few seconds of locking the car.

Also check the left-hand well in the boot for water. You need to remove the trim from the side of the boot, near the tail lamps. The tilt sensor is in there and it doesn't like getting wet. The symptoms don't sound right for it to be this, but it is still worth a check.

Finally, the indicators flashing on unlock indicates that the alarm has been triggered since the car was locked. I do not know why the would flash without - maybe you just didn't hear it?

Cheers R.

[njathind]

Just got in from having a good play with all the different sensors. First off I double checked the radio switch and although it had already been cable tied I unplugged it from the system, I also examined the boot well and found it to be bone dry. Whilst I was there I tested the tilt sensor and managed to trigger the alarm by turning the sensor on it's side.

The bonnet switched seems to be a little sticky so I have lubed it with some WD40 and it seems much smoother, I can now trigger the alarm with the bonnet switch but I will replace it with the X5 switch as I don't trust the switch too much at the moment.

However when I lock the car I still get the LED indicator flashing rapidly for 10 seconds, so I am not sure where to go next with this. When I say I have tested the door switches I have done this by opening and closing each door/boot and seeing if the associated interior light goes out. Is this a good way of testing the alarm switches or is there a more reliable way?

I still don't understand why I get a single flash from the indicators when locking all of the time and only get a double flash when unlocking on the odd occasion.
Also in answer to your first question I have the later alarm with the three buttons on the keys.

Many thanks Nat

A few things to point you in the right direction. I am assuming here that you have the later alarm with the buttons on the key rather than a separate fob.

Firstly the bonnet switch and radio anti-theft switch are wired in parallel. If the bonnet switch has no effect then the radio switch is already triggered. If you have an aftermarket stereo, then it likely hasn't been refitted. I cable-tied mine to simulate the radio being present. You will likely see your alarm LED flash rapidly after locking to indicate a sensor is in the tripped state - which the alarm should then go on to ignore. You want to fix this, as the alarm can potentially be disabled from under the bonnet.

The roof microswitch has nothing to do with the alarm. The protection against the roof being slashed to gain entry is the same as when the roof is down - ultrasonic sensors in the footwells. To test these for a fault you can disable them by pressing the lock button a second time within a few seconds of locking the car.

Also check the left-hand well in the boot for water. You need to remove the trim from the side of the boot, near the tail lamps. The tilt sensor is in there and it doesn't like getting wet. The symptoms don't sound right for it to be this, but it is still worth a check.

Finally, the indicators flashing on unlock indicates that the alarm has been triggered since the car was locked. I do not know why the would flash without - maybe you just didn't hear it?

Cheers R.

[njathind]

Small update, my local dealer had a bonnet switch on the shelf.

£11.00 later and I no longer have 10 seconds of repetitive flashing from the LED indicator, however I still don't get the double flash when unlocking all the time.
Its only ever once in a blue moon...

Any ideas guys???

Many thanks Nat

[siwilson]

I would still look at the radio switch. It can easily 'pop' out of the housing by if the radio had been changed or even the original removed and refitted.

[njathind]

As I have said

Just got in from having a good play with all the different sensors. First off I double checked the radio switch and although it had already been cable tied I unplugged it from the system, I also examined the boot well and found it to be bone dry. Whilst I was there I tested the tilt sensor and managed to trigger the alarm by turning the sensor on it's side.

Is it wise to disconnect the radio switch? As I say the alarm LED flashes at it should.

I would still look at the radio switch. It can easily 'pop' out of the housing by if the radio had been changed or even the original removed and refitted.

[siwilson]

Is it wise to disconnect the radio switch? As I say the alarm LED flashes at it should.

No harm in it. by the time they are in to get the radio the alarm should be going off anyway.

[Robert T]

I think disconnecting the radio switch has the same effect as cable tying it - it is normally open circuit and closes to trigger the alarm.

The single flash on lock, no flash on open is normal correct behaviour for the alarm. If it flashes when you unlock it, it is supposed to be indicating the alarm has sounded since the car was locked - if the bonnet switch was a problem, this could account for it - is it still doing it now that you have replaced the switch?

I had the rapid flashing on mine, and cable tying the switch sorted it. I also had an odd problem with the alarm going off frequently, which turned out to be a label for the alarm system which I disturbed changing some bulbs and it flapped in the breeze right next to the sensor - how do I know? I found the label on the floor of the car one morning and no more alarm problem. LOL.

If everything else is working, then the only other thing to try is disabling the interior movement sensors by pressing the lock button a second time and see if it still does it.

Cheers R.

[Fender2004]

I had trouble with my bonnet switch, and all I did was to place a small sticky pad on the top of the switch. This must have pushed the plunger just a little further down to make the connection.

It worked for me

[robdalej]

Just been reading various posts re alarm switch, mine has just started acting up, when I leave it locked for a few minutes, the alarm will start sounding off. I tested the bonnet switch by holding the switch down , then releasing it slowly, presumably the alarm should then go off but it doesnt, if I disconnect the wire from the switch then the alarm seems to work ok,am I right in assuming the switch is faulty?, also would a switch off any other model fit as i have been quoted £35by local dealer for new switch , seems a lot for a little switch

[njathind]

Just been reading various posts re alarm switch, mine has just started acting up, when I leave it locked for a few minutes, the alarm will start sounding off. I tested the bonnet switch by holding the switch down , then releasing it slowly, presumably the alarm should then go off but it doesnt, if I disconnect the wire from the switch then the alarm seems to work ok,am I right in assuming the switch is faulty?, also would a switch off any other model fit as i have been quoted £35by local dealer for new switch , seems a lot for a little switch

Completely forgot to post back with my remedy, the issue with my alarm was in fact with the bonnet switch. The best way to tell is to connect the bonnet switch and lock the car, keep an eye on the alarm LED indicator. If it flashes rapidly to start with and then slows down to a steady pulse it means one of the sensors is registering an issue. Unlock the car and disconnect the bonnet switch, again lock the car and look at the Alarm LED indicator. If it settles into a steady pulse then you have found your problem.

The bonnet switch is a common part and is shared across many different models, you local dealer is ripping you off at £35. My local dealer, snows BMW in Portsmouth only charged me £11.something with the VAT so something sounds a bit dodgy to me there.\\

Like I say, try the little fault find test I described above and see how you get on.

[robdalej]

ok thanks for that, think I have narrowed it down to the bonnet switch because , having disconnected it , the alarm works fine, have found a few on e bay at around £ 8 s/h, so may try one of those, unless I can find them cheaper at the dealers around Cheshire