S80: Electrical - Alarm issues

hippy996 · Feb 6th, 2024, 13:09

The alarm on my S80 (2012) D2 is randomly going off, when I reset it the brake lights remain on until I start the engine and turn it off again.
I have also just been told that the brake lights were on permanently whilst I was driving yesterday! Any ideas? Thanks!

FreshAir · Feb 6th, 2024, 14:47

Random alarm activations can come from bad connection on the bonnet switch.

Tatsfield · Feb 6th, 2024, 15:20

Copious spraying of the switch with release fluid and then light lubricating oil with PTFE does tend to release the switch if it hasn't been allowed to stay untreated for long.

One way of checking if this is the cause of the problem is to use a 'U' shaped paper clip as a jumper on the female side of the connector to the switch to fool the system that it is closed. Insulate the exposed part of the paper clip to prevent shorting the circuit. The switch is part of the right side bonnet catch and the connecting cable is just behind the slam panel adjacent to the catch. If it is the problem, leave the jumper in place for a week or two before checking if the switch has freed itself. The only downside to this approach is that the bonnet open warning is disabled and the alarm does not cover the opening of the bonnet.

The sticking switch is a common problem but it rarely fails; just sticks until freed.

Kev0607 · Feb 6th, 2024, 15:33

...Could also be the battery in the alarm siren module getting low. That will set the alarm off randomly.

hippy996 · Feb 7th, 2024, 18:50

Thanks all, A few years ago I had the bonnet catch issue and just shorted it out. I think I will have a look though to make sure the connection is still good.
Found out the brake light issue is the pedal, if you touch the brake pedal very lightly the lights stay on, use it normally and they are OK. I will have a look at the switch at the pedal!
I'm guessing the two issues at the same time are a coincidence.

Feb 6th, 2024, 13:09	#1
hippy996 New Member Last Online: Feb 8th, 2024 10:05 Join Date: Mar 2018 Location: Cannock	Alarm issues The alarm on my S80 (2012) D2 is randomly going off, when I reset it the brake lights remain on until I start the engine and turn it off again. I have also just been told that the brake lights were on permanently whilst I was driving yesterday! Any ideas? Thanks!

Feb 6th, 2024, 15:20	#3
Tatsfield Premier Member Last Online: May 2nd, 2024 11:44 Join Date: Nov 2015 Location: Poole	Copious spraying of the switch with release fluid and then light lubricating oil with PTFE does tend to release the switch if it hasn't been allowed to stay untreated for long. One way of checking if this is the cause of the problem is to use a 'U' shaped paper clip as a jumper on the female side of the connector to the switch to fool the system that it is closed. Insulate the exposed part of the paper clip to prevent shorting the circuit. The switch is part of the right side bonnet catch and the connecting cable is just behind the slam panel adjacent to the catch. If it is the problem, leave the jumper in place for a week or two before checking if the switch has freed itself. The only downside to this approach is that the bonnet open warning is disabled and the alarm does not cover the opening of the bonnet. The sticking switch is a common problem but it rarely fails; just sticks until freed. __________________ 2012 XC70 SE Lux Polestar 230 bhp D5 Auto Oyster Grey

Feb 6th, 2024, 15:33	#4
Kev0607 Premier Member Last Online: Yesterday 19:56 Join Date: Apr 2019 Location: Manchester	...Could also be the battery in the alarm siren module getting low. That will set the alarm off randomly. __________________ 2007 S80 2.4 D5 - 110,000 miles

Feb 7th, 2024, 18:50	#5
hippy996 New Member Last Online: Feb 8th, 2024 10:05 Join Date: Mar 2018 Location: Cannock	Thanks Thanks all, A few years ago I had the bonnet catch issue and just shorted it out. I think I will have a look though to make sure the connection is still good. Found out the brake light issue is the pedal, if you touch the brake pedal very lightly the lights stay on, use it normally and they are OK. I will have a look at the switch at the pedal! I'm guessing the two issues at the same time are a coincidence.

Feb 6th, 2024, 14:47	#2
FreshAir Senior Member Last Online: May 3rd, 2024 09:37 Join Date: Feb 2014 Location: Lichfield	Random alarm activations can come from bad connection on the bonnet switch.

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