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What Sensors Could Be Setting My Alarm Offf?


mikester
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the last two nights my car alarm has gone off three times, one time I got in the car to check any messages and just saw "alarm triggered, check vehicle" which doesn't indicate what caused the false alarm.

The next time it happened I did the same, this time I got the message "bonnet open", there's no way my bonnet was open. Checked it, sure enough it was closed tight. I opened it anyway and dropped it shut just to be safe. No more alarms that night. But there was the following night, there's no wind or it wasn't even that cold, what sensor could be setting the alarm off?

Even better, is there a way to check what part of the car triggered the alarm? In the meantime how do I lock the car with the alarm disarmed?

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Sounds like a dodgy bonnet switch to me - have you checked the bonnet switch and wiring?

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Back to my car for lunch... wouldn't you know it, alarm gone off again!

I don't know where the sensor is under the bonnet, if I find it and unplug it will there be any other adverse effects (other than the security or lack of)?

I need a solution to turn the alarm off completely for now as I need a good nights sleep and am concerned about being away from the car for extended periods, anyone?

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Never.

I haven't got my handbook on me, hopefully it'll say in there if I can lock the doors without the alarm. I'm out of warranty now so no chance am I going to the dealer. I'll just disconnect the alarm if I can't find the cause. Not sure how to isolate it without a notification system in the car ie what sensor is fubar!

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Bonnet switch wiring probably looking for closed contact when bonnet shut. If you unplug it this may still make the alarm sound as it will be open circuit (thinking the bonnet already open ?).

If you find connector to switch and disconnect it you will probably have to short out the connection with a piece of cable to simulate switch being in place and bonnet closed. This could be a good test to see if you do in fact have a faulty switch - I would suspect that before a wiring fault.

Switch may just be sticking with colder weather and be fixed with a good squirt of WD40.

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The bonnet switch is part of the latch mechanism mike. If you need a price just let me know

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Kk thanks adam. Will have a look at it tomoz see if some lube will fix it. I've locked the car with the key in door and used a disclok in the meantime, not sure if that doesn't activate alarm

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Hi, did you resolve this?

I have just bought a Fiesta Zetec S and am finding the alarm is going off too! It went of twice last night!!

I am taking mine in next Wednesday as still under warranty but is there a quick method you found out? I need sleep!!

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  • 1 month later...

anyone have any joy solving this, my alarm is now going off each time i look the car, various messages bonnet open, door open, boot open etc!!! grrrr!!

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  • 2 weeks later...

if you have a radio code try disconecting the battery for half hour or so to reset the alarm module otherwise if you knew where the module was under the dash you could just disconect if in place of the battery. the bonnet catch is indeed inside the latch and sometimes the grease inside it when its cold or old gets sticky and makes it read wrong.. but the member with varous faults needs the module disconnected and reset or replaced if its went faulty and wd40 for the bonnet faults should wash and free it up. as for locking without arming the alarm if you pres the remote once so the doors lock and DO NOT press a second time as the alarm arms with the double locking, well it used to on the fiestas before the current model,lol..

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  • 11 months later...

Anyone try and figure this out?my dealer gets the part but is the wrong fitment.all he does is wd40 or resets it.last for 4-6 months then prob will have to do again.happened twice now.this is frustrating for me as I'm a driving instructor.cant risk this message coming up while test is happening.back to my 08 plate fiesta style,no sensors no headache.going to pickup my faulty car today.not looking forward to teaching in it again.

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You have PM.

It's a piece of pee fix, don't mess about disconnecting anything. Just buy a new latch, haven't had the warnings and false alarms since I replaced the latch at the start of last year.

Around £30 for the latch with perimeter sensor from fordpartsuk.com (sorry Adam, I know I should have come to you first!)

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  • 6 years later...

Hi we have a ford fiesta 2015 model after it was taken for a valay alarm keeps going off...its not under warranty anymore but we losing sleep over this stupid thing that goes of every 15 mins please help what can we do

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20 minutes ago, Fordfanatic123 said:

Hi we have a ford fiesta 2015 model after it was taken for a valay alarm keeps going off...its not under warranty anymore but we losing sleep over this stupid thing that goes of every 15 mins please help what can we do

Do you get any warning messages on the dash for either the door, boot or bonnet being open?  Faulty switches on any of those can set the alarm off. 

You'll also have interior proximity sensors that you should be able to switch off, as if you'd left a dog in the car for example.  I'd suggest cancelling those for one night and see if the alarm still triggers.

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  • 6 months later...

I have a brand new 20 plate Ford Fiesta I went to get it cleaned today first time since I got it from March and my alarm just started going off at 1am checked it no one has been near it turned it on and off locked it and it kept going off so had to keep in locking and locking it again using the fob key it has now stopped but I’m wide awake terrified it will go off again when I got it washed has it done something to the sensor? 

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Any chance a fly or a bug has got inside your car that you have not seen? Worth a check when it is light.... 

Just avoid the neighbours for a while. 🤣

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Not sure I’ll check in a few hours yeah I will hahah thanks , when the deal ship opens again I’ll take it down just to check it out make sure there is nothing underlying hope to god it doesn’t go off tonight it was so dirty with being on lockdown here me thinking getting it washed was a good thing hahah . 

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Did they clean the interior?  If they had all the doors open it's probably flattened the battery.  Or let a moth in as suggested above!

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It will take a dealer or anyone with the correct diagnostic equipment about one minute to connect the car up and read what has triggered the last four alarm events.

If a pressure washer was used to clean the car, best to tell them because if it was used over enthusiastically water may have got somewhere where it should not have. 

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No they didn’t do inside it was a wash and go but when I got home I wiped over it the buff and shine it and yes they did use a jet wash on it , Ford aren’t open until 1st June at the earliest so just hope it doesn’t keep going off of a night. 

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It is good practice to take a car for a good run after washing even without a pressure washer because a lot of water can get left in the nooks and crannies although it should not cause the alarm to trigger.

If it does not happen again I wouldn't be that bothered about getting it checked unless you are getting something else done because the dealer may attempt to charge you for the diagnostics. 

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I made that mistake with the Mk6 ST once...gave it a proper good clean with the jetwash, engine bay and everything, ready for a car meet the next day....got in the next day and it wouldn't start!!  Massive list of fault codes, too many to work out what the issue was.  

Took the Focus Titanium to the meet instead, much to the disappointment of everyone there! :laugh: 

Day after that, I got in the Fiesta to start fault finding, turned the key and it fired straight up!! Obviously something just got damp and needed to dry out...

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  • 1 year later...

I have been up since 5am... car alarm. No reason just because it thinks I need less sleep!! My immediate neighbours are even closer to offending car so I guess I will need to get some wine. 

Been reading all the post above... this is an ongoing thing with a wider issue for me. I had the car for diagnostics and TWICE i was told and shown there is NOTHING wrong with my car BUT I know there is something wrong... 

1. Alarm goes off randomly without reason. 

2. Boot open signal - yet it is closed. 

3. Aircon only blows warm air even though set on cold. 

4. Hazzard Lights stopped working

5. Power Steering have died twice on me in the past year only to work after I switched off and start again. 

 

This all points to some electrical fault. I am no mechanic, I dont even know how to explain this to a mechanic. My brother in law suggested I replace the positive battery connector cable as this is something he has experience? Any other suggestion? 

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