IS300H - Alarm going off

route66 · July 16, 2021

I have a 2014 IS300H and the Alarm has started to go off recently for no apparent reason. I've had the car for about 4 years with no issues to date.

It has only happened about 4 times and all of these in the last month. Typically, it happens about an hour after parking up and this after using the car for anywhere from 30 minutes to 2.5 hours.

As an interim measure, can the alarm be disabled (handbook only talks about disabling intrusion sensors - e.g. if leaving a dog in car)?

Could this be a 12V Battery issue? The car is on its original Battery but this has shown no problems to date and the car has generally seen at least an hour of use weekly - despite Covid.

Appreciate any help - it woke me at 4:30 this morning and I've been awake since searching for answers. 😮

PRT68 · July 16, 2021

Most probably the 12v Battery. By the time the winter weather comes, at 7or8 years old It's bound to leave you stranded anyway. So, whilst you're still mobile, get one fitted at a Toyota or Lexus dealer. There have been instances of radio problems after a new Battery has been fitted, so let them do it , rather than anyone else. If you still have alarm problems, at least you will have eliminated the main culprit.

ColinBarber · July 16, 2021

If you have a volt/multi meter then measure the voltage of the 12v Battery before putting the vehicle in Ready mode - the voltage has to be quite low for the alarm to trigger.

It may very well be a spider, insect or a 🐍 🙂. Just turning off the interior sensor is the best way to determine if it is interior movement, which is the most common cause for false alarms, or something more serious such as a sensor or Battery issue.

route66 · July 16, 2021

Thanks for the replies.

My scenario is that if I put the alarm back on, say, an hour after activation, it doesn't go off again. I think this means that if it was the Battery voltage triggering the alarm, it would be some sort of temporary voltage instability. If that's even a thing? As mentioned, I've had no issues whatsoever with the 12V Battery to date - and I've read lots of threads on here of people who have so I know this is thing. The manual does say this about how the Battery can trigger the alarm:

If I lock the car with the mechanical key (never done this before), will that leave the alarm off?

I have a multimeter and will check the voltage from the boot Battery terminals later today. If I don't come back on this thread, it means it was actually a 🐍 😲 ...

route66 · July 16, 2021

Answering one of my own questions above - just saw this on page 550 of the manual:

And while I'm here - Page 99 states how to disable the intrusion and tilt sensor:

royoftherovers · July 16, 2021

4 minutes ago, route66 said:

Answering one of my own questions above - just saw this on page 550 of the manual:

You are a star !

You have unlocked one of Nature`s most secure secrets and you have been awarded 50 fictional points.👍👍

If only we had more Members like you !

route66 · July 16, 2021

Thanks John - I know you like references to the manual 😉

I'll post my findings on the Battery later ...

Thackeray · July 16, 2021

On 7/16/2021 at 8:50 AM, ColinBarber said:

It may very well be a spider, insect or a 🐍 🙂. Just turning off the interior sensor is the best way to determine if it is interior movement, which is the most common cause for false alarms,

My alarm has gone off a few times over the years. Same car as yours. It's always been an insect in the car.

My solution has always been to turn off the movement sensor for a day or two until the insect escapes or dies.

I particularly liked the story another contributor described on a similar thread. His alarm would go off at 1.30am each night to his great annoyance. Couldn't find the solution. Eventually his wife cracked it.

Around 1.30 am each morning a fox strolled down the pavement outside the house. The next door neighbour had movement sensor floodlights and the fox passing by turned on the floodlights. The bright light made a moth in the car think it was daytime and it started fluttering about. The car thought there was an intruder and set off the alarm.

Spacewagon52 · July 16, 2021

1 minute ago, Thackeray said:

My alarm has gone off a few times over the years. Same car as yours. It's always been an insect in the car.

My solution has always been to turn off the movement sensor for a day or two until the insect escapes or dies.

I particularly liked the story another contributor described on a similar thread. His alarm would go off at 1.30am each night to his great annoyance. Couldn't find the solution. Eventually his wife cracked it.

Around 1.30 am each morning a fox strolled down the pavement outside the house. The next door neighbour had movement sensor floodlights and the fox passing by turned on the floodlights. The bright light made a moth in the car think it was daytime and it started fluttering about. The car thought there was an intruder and set off the alarm.

Cracking story! Amazing they found it out.

route66 · July 16, 2021

It's reading 12.27V:

... which according to this diagram posted in the is300h battery problems thread:

... means my Battery is ok (or at least ok'ish).

I had a quick look around the car opened all the doors, boot and bonnet but didn't see any insects - or snakes!

Because this has only recently started to happen - and then very intermittently - I guess I'll have to do some experimenting but I might have to wait for a month before I can conclude anything.

Unless anyone thinks it could be the Battery or some sort of voltage instability ...

ColinBarber · July 16, 2021

8 hours ago, route66 said:

Unless anyone thinks it could be the battery or some sort of voltage instability ...

Nope I really don't think so, and whilst your voltage is a little low it would need to be down < 11v to trigger the alarm voltage sensor, at which point you would struggle to power up the vehicle again so I'd rule out the Battery for now.

Kiefels · July 19, 2021

All this info here, is why I became a member of LOC UK.

I only purchased my car on Thursday 15th July 2021 (For those reading old posts) 2013 F-Sport with almost 36,000 miles on it

First day my Alarm went off a 23:00, next day, nothing, day after 23:00 awaiting what happens this evening. Was thinking a cat may trigger it but as I have CCTV around my house, I have not actually seen one in the area at that time.

A quick voltage check on the Battery puts it in the green zone but that was after a run so I will check it again in the morning.

I'll keep you in the loop if I find anything

Joe43 · July 19, 2021

Bought my IS300h in Dec last year and not had any problems until a couple of weeks ago when the alarm went off for no reason.

Happened twice first during the day when just the alarm sounded then the following night when alarm, lights and horn sounded. Took car to Lexus Leeds and after checking it over have arranged to replace the alarm this Thursday under warranty. Not sure if it's part of or all of the alarm they are replacing but will report back.

route66 · July 20, 2021

16 hours ago, Joe43 said:

Happened twice first during the day when just the alarm sounded then the following night when alarm, lights and horn sounded.

I didn't know there was a separate Alarm sound. Mine sounds the horn and flashes the lights - the indicators at least, not sure about the headlights

Joe43 · July 22, 2021

Quick update.

Today Lexus Leeds replaced internal intrusion sensor, collected car this morning brought it back mid afternoon fully valeted with new sensor. Very impressed with their service.

Kiefels · August 1, 2021

I'm still working on a solution.

Checked the Battery after vehicle has sat for several hours. Still reading ok @ 12.3 v

Issue has primarily showing in the evenings, first off all at 11pm every other evening, then at 10pm every other evening. Only the over, up until last night, when it went off twice, whilst at work.

tonight I will disable intrusion sensors and see what happens

Kiefels · August 17, 2021

On 8/1/2021 at 5:29 PM, Kiefels said:

I'm still working on a solution.

Checked the battery after vehicle has sat for several hours. Still reading ok @ 12.3 v

Issue has primarily showing in the evenings, first off all at 11pm every other evening, then at 10pm every other evening. Only the over, up until last night, when it went off twice, whilst at work.

tonight I will disable intrusion sensors and see what happens

***UPDATE***

I disabled the interior sensors for 3 whole days and nights, then allowed them to activate after that.

So, far, no false alerts and waking of neighbours. Been over 2 weeks now.

This leads me to two conclusions:

1. There was some critter, moving around in the vehicle and setting it off. It died or left the building.

2. Disabling the interior sensors removed a glitch in the sensor system.

Unable to conclusively disprove either of those, so, as Toyah Wilcox would say..

It'th a mythtery!

Apologies to those not akin to the reference or are offended by humour.

Mincey · August 17, 2021

10 minutes ago, Kiefels said:

Unable to conclusively disprove either of those, so, as Toyah Wilcox would say..

It'th a mythtery!

Apologies to those not akin to the reference or are offended by humour.

If as you say it could have been a critter, should you have said "it'th a mothtery"?

route66 · August 17, 2021

As the OP, I felt duty-bound to post an update to this thread but shied away - didn't way to tempt fate and all that.

Anyway, it's been about a month since the last activation. The week after it started happening, I locked the car with the key to avoid switching on the alarm and then started to just disable the intrusion sensor before locking up on the button. I've got increasingly confident in the last couple of weeks and just (double) lock it normally.

Hopefully ColinBarber and other were correct in their predictions above and the critter is now dead.

To paraphrase Scooby Doo: Thanks for getting involved until the mystery was solved 👍

Maxz · June 30, 2022

Sharing my recent experience of the super natural...

One week after my IS' 7 year birthday, same experience as others, as the light and temperature dropped at night, my alarm was sounding off. My drive is south facing, rear of car facing the sun, super hot daytime, cold at night. I pretty much strip searched the car, not a critter to be found, the next night repeat performance, again no pest could be found the next day. The third night I disabled the sensors (tilt and intruder), alarm did not fire off. Did this until I replaced the Battery, now fully armed no issues.

So I accept maybe this bug could hide itself so well I may not have found it, but another thought, is there potentially enough draw from the tilt and intruder sensors being on, if the Battery is near end of life, they could just bring the voltage down enough to trip the alarm? Disabled the draw is slightly lower so no trip? Again speculation as I did not check the voltage on the original Battery and a longer trial would be needed to prove it out.

If you have a voltmeter diagnosis is easy. If not, maybe the best procedure is strip search (or fumigate!) your car, lock it for a week with the sensors disabled. Rearm after a week, if no sounding, it was a bug, if sounding off resumes, may well be the Battery, especially if you know it is the factory original.

Maxz · July 2, 2022

Note for the last process, use the secret menu also, because a low voltage reading there will also help determine if the Battery is nearing it's end. Secret menu trick worked, should have checked the old Battery but the new one reading 13.7 volts on idle(nothing electrical on), so well in the green on the Battery chart given it is new. Lexus Parts Direct current price as at July 2022 is £145 including delivery. Gold members have a discount though I believe.

Maxz · July 26, 2022

For the first time ever I am also reaching 52mpg, when in the past 3 years no matter how economically I tried to drive, 47mpg was the best I could achieve. Seems if your 12v aux is old, a certain amount of energy must be getting "wasted" as the system keeps trying to charge the aux Battery to a certain voltage level, that maybe it can't reach anymore. With a new Battery in the healthy voltage range (and holding charge), the system possibly retains/charges more energy into the hybrid Battery instead, thus increasing your range. Might be a bit of a far fetched theory given how small this AGM aux is, and I wonder how accurate the mpg monitoring really is.

I am loving the secret menu, because instead of having to trickle charge at random, I can just monitor when the voltage drops out of the top band and stick it on just to top up. Great time saver only having to setup the charger when it is actually needed.

agent_dess · July 27, 2022

13 hours ago, Maxz said:

For the first time ever I am also reaching 52mpg, when in the past 3 years no matter how economically I tried to drive, 47mpg was the best I could achieve. Seems if your 12v aux is old, a certain amount of energy must be getting "wasted" as the system keeps trying to charge the aux battery to a certain voltage level, that maybe it can't reach anymore. With a new battery in the healthy voltage range (and holding charge), the system possibly retains/charges more energy into the hybrid battery instead, thus increasing your range. Might be a bit of a far fetched theory given how small this AGM aux is, and I wonder how accurate the mpg monitoring really is.

I am loving the secret menu, because instead of having to trickle charge at random, I can just monitor when the voltage drops out of the top band and stick it on just to top up. Great time saver only having to setup the charger when it is actually needed.

Pretty wild theory... thought all the 12V Battery does is help start the car and few other bits and pieces, not utilised to the extent it would it would in a normal car.
I would assume if you had dying cells replaced in the hybrid Battery that would be reason you would see mpg boost.

Maxz · July 27, 2022

12 hours ago, agent_dess said:

Pretty wild theory... thought all the 12V battery does is help start the car and few other bits and pieces, not utilised to the extent it would it would in a normal car.
I would assume if you had dying cells replaced in the hybrid battery that would be reason you would see mpg boost.

Yeah, logic does not seem to dictate a 5mpg benefit just for replacing an old 12v aux with a new one. I think the mpg reading you get is only accurate to an extent. I'll give it a bit longer and maybe after a few shorter drives it will level back out at 47mpg, let's see. I reset the mpg counter a few months after I first bought the car too, however on the original Battery, it never got as high as 52mpg at the initial reset, it started high 30's and worked it's way up to platau off around 47mpg instead.