Hi my ford focus 2019 keeps setting off the car alarm off every 15 minutes of the vehicle being locked. Took it to ford and they can't find the fault with it. When the alarm kept going off I had to disconnect the negative battery terminal for it to stop alarming.

When 'Ford' checked it out, do you  know if they hooked up your car to read any stored digital fault codes? (like a faulty bonnet sensor, most common cause)

Yes they put there diagnosis on it and found nothing they still has it now. Took the battery off when it was alarming and now its behaving itselves but this has happened twice in a month now with the car alarm randomly going off 

5 minutes ago, JPP_2000 said:

When the alarm kept going off I had to disconnect the negative battery terminal for it to stop alarming.

That in itself is very odd. The Focus Mk4 has a back-up battery which is part of the sounder hidden under the 'bin bag' full of foam between the inner and outer wing on the passenger side.

Disconnecting the car battery should not stop the alarm from sounding, otherwise a car thief could simply disconnect the battery and tow it away (if they really wanted to steal it).

My guess is that the alarm back-up battery in the sounder is almost flat, and is triggering the alarm. I would have expected that a good Ford dealer would have been able to check that. If you use a laptop and FORScan you will be able to read the last 3 or 4 alarm activations which will say why the alarm was triggered.

I stop the car alarm by unlocking the car and locking it again but to disconnect the battery I have the leave the vehicle unlocked. Could it be the BCM that causing this?

1 hour ago, unofix said:

My guess is that the alarm back-up battery in the sounder is almost flat, and is triggering the alarm.

Good to hear that alarms still have that feature. 30 odd years ago I had installed a LaserLine 996 alarm which had the built in battery. When car left in for service, I always disabled it (using a mechanical key on the sounder) so it wouldn't upset the garage by going off if main battery disconnected...

2 hours ago, JPP_2000 said:

Could it be the BCM that causing this?

I though that I'd said that it was likely to be a problem with the back-up battery. In order to find out what the problem is and not just a guessing game you need to use FORScan and get the Ford specific DTC's which should give a reason as to what triggered the alarm.

It could be the BCM, the bonnet latch, a faulty door lock or a flat back-up battery, etc. etc, but it needs to be investigated logically.

On 1/2/2025 at 8:53 PM, unofix said:

I though that I'd said that it was likely to be a problem with the back-up battery. In order to find out what the problem is and not just a guessing game you need to use FORScan and get the Ford specific DTC's which should give a reason as to what triggered the alarm.

It could be the BCM, the bonnet latch, a faulty door lock or a flat back-up battery, etc. etc, but it needs to be investigated logically.

My 2020 Focus has been doing this over the last few months on and off. I took it to the local Ford dealer, and they couldn't find anything, then wanted £430 to remove interior roof lining and check wiring? I declined the offer... 

I had the car washed yesterday and in the evening, it went off again first time for a few weeks... Very annoying as the alarm keeps going... I thought they were supposed to silence after a given time?

The answer is use FORScan and it will give a reason for why the Alarm was triggered.

On 4/7/2024 at 8:59 PM, unofix said:

FORScan (for use with Windows Laptop) : https://forscan.org/download.html

It's what many Ford owners use including some Ford technicians.

vLinker FS, cable for laptop: https://www.amazon.co.uk/Vgate-vLinker-Adapter-FORScan-MS-CAN/dp/B0952P4MLP

vLinker FD, for android phone: https://www.amazon.co.uk/Vgate-Bluetooth-vLinker-Scanner-Diagnostic/dp/B08H82WC8L

vLinker FD+, for iPhone: https://www.amazon.co.uk/Vgate-Bluetooth-vLinker-Scanner-Diagnostic/dp/B08H8JHWP2

 

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