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R Gordon
R Gordon,
Category: Mazda
Satisfied Customers: 1
Experience:  Mechanic at RAC Motoring Services
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Car alarm keeps going off, but no particular pattern as to

Customer Question

car alarm keeps going off, but no particular pattern as to why. I have changed battery in key fob. Car is 2010 reg
JA: Have you changed a battery before?
Customer: a key battery yes, the car battery, no
JA: What is the model of your '10 Mazda?
Customer: mazda 6 elite
JA: Are you fixing your Mazda2 yourself? What have you tried so far?
Customer: just changing the battery in the key fob
JA: Anything else you want the Mechanic to know before I connect you?
Customer: no, thanks for asking
Submitted: 15 days ago.
Category: Mazda
Expert:  R Gordon replied 15 days ago.

This can be due to a battery drain, Check the boot light and glovebox lamp are not stuck on, also check the bonnet and doors all close

as they should.

Hope this helps


Customer: replied 15 days ago.
Thank you. Glovebox doesn't have a light. Boot does. It was switched off, but came on ok when i turned it on. Have now turned it off again. Everything properly closed too. What next??
Customer: replied 15 days ago.
Can I please just understand what is happening now as nobody has responded. Do I not get a further response now unless I spend another £16, even though the solution suggested hasn't resolved the problem? Or is everyone just busy?
Expert:  R Gordon replied 15 days ago.

Hi just to let you know I work from home in between doing other stuff nobody is on here permanently to help sorry just being honest

So I need to know are you using the car every day is it starting up ok or is the battery struggling a weak battery will cause

alarm faults because of voltage drop, Also you might need to do a battery reset (disconnect battery for 20 mins)


Customer: replied 15 days ago.
Thanks for getting back to me. That's fine. I just didn't know how the system worked. I'm not driving it every day at the minute as working from home, but whenever I do use it, it starts fine. I probably drive it every 3rd day or so, but only short distances.
Expert:  R Gordon replied 15 days ago.

Hi just logged on this morning, So has this problem only started since lockdown ?, It could be that your battery is degrading

when you start a engine the starter motor typically draws 250-300 amps to turn the engine over and then once started the alternator

has to recharge what you just used so the charge going back in will be anything between 30 to 10 amps depending

on various factors like battery condition and alternator output and consumers in play like heater blowers, heated windows etc,

so if you are only doing short runs occasionally it will put a huge strain on the battery and it could cause an older battery

to lose voltage over night and the volt drop can trigger alarms, Your battery is probably only receiving what is deemed to be a surface

charge and probably is just enough to be able to start normally if you continue this pattern eventually the battery wont start the engine ,

so I am going to make an assumption about your battery assuming your car is petrol engine the battery would be approx 400amp reserve capacity

if you had to charge a 400amp battery fully at 10amps it would take 40hrs 40x10 = 400 this is just my example to give you a guide if your vehicle

is diesel its worse for the battery in terms of load on starting etc, This is not necessarily going to be your problem but in my experience most problems

of alarms going off are caused by either a drain on the battery such as boot light stuck on etc or faulty worn out car battery, there are things that can be done by a decent auto electrician to fault find such as fit an inductive current clamp on the battery wiring to see if there is a drain etc but it may be

the battery just needs a proper charge or replacement you could call someone like the RAC out to do a proper battery test as its unlikely the alarm

system is faulty.

Hope this helps Richard