Alarm going off randomly at night only

R

Rob64

New member
Hi,

Hoping someone can help out with an issue that has only been happening for the last couple of months.

The factory fitted alarm has gone off a number of times and always happens at night and the most inconvenient times. I’m thinking it may be outside temperature related and or a faulty sensor which gets triggered when the temperature drops.

Have looked through a few threads and can’t see any results which are identical and I’ve tried looking at the settings and can’t find where the security settings are kept to see if there’s a dodgy sensor or a reset needs doing. Annoyingly there’s no set pattern when the alarm goes off and can go day’s week without any issues.

Anyone got any suggestions/ideas?
 
I have a few thoughts:
1. Is there anything in the car's interior which could fall off or become detached in colder weather? eg. Phone holder with suction cup to windscreen. Something like this falling off would set off the alarm;
2. Does your dashboard show any information when you switch on after an alarm event? It should show what triggered the alarm;
3. The battery back up sounder (BBUS) can give problems, see https://www.ftypeforums.co.uk/viewtopic.php?t=6397 When double locking the car, do you get a beep? If not, this indicates an alarm fault. If you've got as far as this, the next step is a scan for fault codes via OBD port.
 
Thank you for the advice.

Nothing hanging in the interior which could set it off but good shout, hadn’t considered that.

Nothing on the dash that alarm was activated.

I get the beep on double lock but rarely do double lock, maybe I need to do this on a regular basis and see if that helps.

I think you’re right that need to do the diagnostics as next steps. Thanks again for your help, much appreciated
 
May not be related but personally I always double lock as it gives better security and why not. Mainly I do it because I always have for more years than I remember.

Strange that the dash doesn't say it was activated, that makes me think it isn't a faulty sensor but more a fault with the alarm control (beyond my knowledge of where that is). If the sensor was giving a false alert then the car would react (give the alarm) and presumably record that it happened and what set if off?

If you hadn't said that then I would have said a faulty sensor, when I was previously and engineer at Honda there was a period when the interior sensor would prompt the alarm in cold weather and those were a faulty sensor.

Alternatively could be a spider roaming around inside.
 
AFAIK double locking allows the car to shut down fully, thereby prolonging battery charge. Low battery on these cars throws up all sorts of odd electrical effects.
 
Many thanks guys for your help, especially the double locking piece. Let’s see how it goes, no issues last night.
 
Common problem on car alarms is the under bonnet switch malfunctioning. Affects many makes and models so I’d take a look at it and see if it well connected, and operates. I assume as it’s under the bonnet, more heat cycles, damp, dirt, etc.
My old Z4 had this and would go off randomly and was so frustrating, wasting time testing things.

If you still keep getting alerts and don’t want to run diagnostics this is just a £25 part to swap out and probably returnable..
Not sure if it push or magnetic,.

Part looks generic. Jaguar F-Type XJ XK Genuine part C2D27159
Check you VIN though
 
Thanks for advice re bonnet. As it happens alarm went off again last night and this time the dash highlighted that it was from the bonnet sensor. Lifted the bonnet and couldn’t see anything obvious but also couldn’t locate where the sensor actually is. When shutting the bonnet the car failed to then lock and the dash stated bonnet is open even though it had fully closed.

I then slammed it harder and could then lock ok. Ive unchecked alarm sensor setting for now and may invest in diagnostic kit or it’s due a service soon and have Jaguar check it over
 
Are you closing the bonnet in the "correct" way? A shown in the handbook - pushed from the front with hands between the vents (or higher if AWD).
 
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