Alarm Keeps Going Off On Rx400h

Mr Pants! · May 11, 2009

Thought I would share this with you, sorry if that has been posted, I did search and could not find anything......

I went to get into my car this morning, pressed the unlock button and the alarm went off, but the doors did not open. I tried pressing all the buttons, nothing, it just kept screaming at me. So I unlocked the doors manually, got in and tried to turn on the ignition, got the engine management light on and that is all, no Ready light came on, alarm was still going off.

So I went and got the other keys I have, the grey and black keys, they had not effect either and appeared to be fully charged, so I could not shut the thing up.

Then after about 5 mins, the alarm stopped and there was a continuous loud clicking under the bonnet, a bit like my four way flash should have been working but they were not illuminating.

So I called my Lexus dealer who suggested it was due to wireless interfearance in the area, not convinced on that. So I called the Lexus roadside cover out and straight away that chap said, "Flat car battery".

He lifted the bonnet and took the plastic cover off so he could show me the Battery, there is a little optic indicator on the Battery that indicates its state, my Battery clearly showed "Charge was necessary" which is indicated by a red dot surrounded by white. He connected the booster charge pack thing from his van and straight away the car remote worked and everything sprung into life.

The problem with my car is due to me doing a lot of very short journeys where I am not passing 25mph, so my engine does not kick in very much at all, especially with all this nice weather I have not been running my air con or anything, just open the sun roof and go.

The other two indications the optic tells you is:

All red with white dot = needs topping up with water

All blue with red dot = Is OK

All white with red dot = Charge necessary.

I now have the car on trickle charge to sort the problem.

Hope this helps anyone who end up in this situation. :)

gomailbox · December 28, 2017

Thanks a lot Mr Pants. Mine played up last night at 1am woke up the entire neighbourhood. Did not know what it was causing the alarm so tried turn it off and on a few times and it went off again and again. Mate I was stressed.

After reading your post, replaced the Battery and bam its gone. Thanks for taking time to share this info.

Bijan41 · July 15, 2021

I have a lexsus rx 450h 2011. The alarm has started goin off mostly at night. It has done it 5 or 6 times in the last two months. Once it was during the day. It goes off for 5 seconds then it stops. The doors remain unlocked during this. I have contacted lexsus they say to try turning the sonar off when locking the car but i cant do this all the time as i forget. They wanted to know if there is a problem with the sonar. What do you recommend.

AWF · July 16, 2021

I know just how you all feel. Same model same year. My granddaughter goes to school 4 miles away from my home. All roads to her school are 20mph and usually have queuing traffic so even if speed was 30mph I would really would have the engine running. It takes me about 25 minutes to travel that 4 miles and always have 2 mauve bars on display for hybrid Battery. I have to sit in "Ready" mode and run the engine trying to charge hybrid Battery before we leave school grounds. As we only use the car for shopping trips and collecting granddaughter one day a week I often have low reading on 12 volt Battery. Any reading below 12.22 volts generates three error code readings Check Hybrid System, check AWD and check VSC systems. My technician has checked with tech stream and found no codes to cause this. Clear the codes and charge Battery car runs OK. New Lexus Battery fitted with same problems. Is this a design feature?

ColinBarber · July 16, 2021

4 hours ago, AWF said:

I have to sit in "Ready" mode and run the engine trying to charge hybrid battery before we leave school grounds.

Why? You don't have to worry about the charge level in the hybrid Battery.

Herbie · July 17, 2021

20 hours ago, AWF said:

I have to sit in "Ready" mode and run the engine trying to charge hybrid battery before we leave school grounds.

As Colin asks, why do you do this?

Many millions of Pounds have been spent in the development of an amazingly intelligent and complex hybrid system so just let it do it's job - it will decide when to run the petrol engine and when not to run it.

20 hours ago, AWF said:

As we only use the car for shopping trips and collecting granddaughter one day a week I often have low reading on 12 volt battery

Could you not connect a trickle charger to the Battery so that when the car isn't in use at least it will keep the 12V Battery up?

Alternatively, could you not just 'invent' reasons to use the car more? Just go out for a nice pleasure drive without any particular purpose in mind?

All car batteries will deplete if left long enough but given that Lexus only fit small ones in their hybrids it's a problem that seems to affect us more than others. Sadly, it's just something that we have to live with but at least being aware of it means that we can take the steps above (trickle charge or use the car more) to mitigate the problem.

Barry14UK · July 17, 2021

My next project, when I can find the time, is to fit a camper type socket to the rear of my car that would feed 240v supply to the smart charger in the boot connected to the 12v Battery. There is a convenient tie down leg at the rear that would be handy. So I will just need to hook this up from time to time to my external power supply. This could also be helpful if the Battery dropped to a level that it would not prime circuitry to connect to the traction Battery.

There are occasions when the car is not used for some time so this could be of benefit.

Barry14UK · July 17, 2021

My alarm went off the night before last but I had locked it with windows partway open to keep temperature down for when used early yesterday morning. So just closed windows and turned off alarm. My wife found something crawling on her seat the next morning so likely this was the cause - which reminds me, I must spray the interior - don't want insects populating car and triggering alarm.

Herbie · July 17, 2021

45 minutes ago, Barry14UK said:

My next project, when I can find the time, is to fit a camper type socket to the rear of my car that would feed 240v supply to the smart charger in the boot connected to the 12v battery.

As I pointed out to someone else who was thinking of doing this, you're better off mounting a weatherproof box on the wall (assuming you park on the driveway) and putting the charger in there so that you're only passing around 12-14V into the car rather than mains voltage.

If it was mains voltage and you forgot to unplug it one day before driving off it may get quite interesting :laughing:

Barry14UK · July 17, 2021

7 hours ago, Herbie said:

As I pointed out to someone else who was thinking of doing this, you're better off mounting a weatherproof box on the wall (assuming you park on the driveway) and putting the charger in there so that you're only passing around 12-14V into the car rather than mains voltage.

If it was mains voltage and you forgot to unplug it one day before driving off it may get quite interesting

I can't recall having seen this aspect mentioned previously but it is a valid point, so thanks for mentioning Herbie. Is there a way I can adopt your suggestion but stop anybody using the external feed socket on my car to draw current from my 12v battery when I am parked somewhere, one way diode or something? This possibility is avoided if the smart charger is in line with the Battery within the car but has the disadvantage you mention.

ColinBarber · July 18, 2021

11 hours ago, Barry14UK said:

Is there a way I can adopt your suggestion but stop anybody using the external feed socket on my car to draw current from my 12v battery when I am parked somewhere, one way diode or something?

I'd not recommend using a diode because the 0.6 V drop across it would mean the charging voltage at the Battery is not correct. Maybe fit a little switch inside which breaks the circuit when you don't want to use it.

Also fit an inline fuse so that if the socket/external wiring is shorted it doesn't damage your Battery or melt the internal wiring to the socket and start a fire.

Herbie · July 18, 2021

11 hours ago, Barry14UK said:

Is there a way I can adopt your suggestion but stop anybody using the external feed socket on my car to draw current from my 12v battery when I am parked somewhere,

I don't think I've ever seen a random guy looking for 12V sockets at the back of cars in a supermarket car park (or any other car park) so first of all, someone would have to know that a socket is there. Secondly, you could use something like SpeakON connectors that are keyed - this is the type that I used in my last RX to create a convenient jump start point in the cabin:

Plug

Socket

These are rated at 30 or 40A so way more than capable of doing the job.

EDIT - just be careful Barry, I've realised that I linked to the wrong socket as that one is for PCB mounting but you'll need one for panel mounting. I'm almost sure that you can buy the sockets with front a front flap to protect it from the weather too but I'm just about to go out and haven't got time to find it.

Barry14UK · July 18, 2021

Colin and Herbie - thank you for your input - much appreciated. It gives me options to consider.

ColinBarber · July 18, 2021

17 minutes ago, Herbie said:

Plug

Socket

These are rated at 30 or 40A so way more than capable of doing the job.

EDIT - just be careful Barry, I've realised that I linked to the wrong socket as that one is for PCB mounting but you'll need one for panel mounting. I'm almost sure that you can buy the sockets with front a front flap to protect it from the weather too but I'm just about to go out and haven't got time to find it.

I was just going to state that the socket is fine for interior placement but certainly not suitable for exterior as it has no IP rating/moisture protection. That last thing you want is water to get into it and actually cause a parasitic drain on your Battery.

Herbie · July 18, 2021

10 minutes ago, ColinBarber said:

I was just going to state that the socket is fine for interior placement but certainly not suitable for exterior as it has no IP rating/moisture protection. That last thing you want is water to get into it and actually cause a parasitic drain on your battery.

I agree Colin but it just gives Barry more ideas to play with.

John Wiechman · August 8, 2021

Alarm goes off, drains Battery, no mechanics can figure it out! 2008 Lexus 400H. Best solution is to not lock the car. Last night we locked the car and alarm went off and fan would not go off, so Battery drained and car would not start. Ideas, anyone?

MartinH · August 8, 2021

Here's a thought. My IS250 suffered from very similar symptoms to those described. Eventually Sunil, the chief tech at Lexus Edgware Road, tracked it down to a blocked drain pipe from the sunroof surround. Water runs out into the engine bay and fritzes the electrics. He said he'd never seen it in an IS250, but had seen it several times in an RX (I think). His solution is to clear out the drainpipe with a pipe-cleaner.