IS300H Electrical gremlins (car thinks its still on when ignition is off)

Josh86 · March 17, 2022

Hi all,

I've been a long time lurker of this forum, but im now in need of help with a strange issue. Owned the car for a year and a half with no issues until this weekend gone.

1. Got home one night and locked the car as normal and went to bed, I was then woken up by the alarm going off.

2.Turned it off but it proceeded to do it 4 times that same night, then I noticed (on the last alarm sounding) that the key would not lock or unlock the car. Took the negative Battery terminal off(had to use the physical key to get in the boot) and all was good, or so I thought!!

3. Put the Battery back on and even though the car had been off all day, the car said ''key not detected''. The climate control was also running as was the headlights(set to auto mode). So the car thinks the ignition is still on?

The car still starts and drives with no lights or errors on the hybrid system. Its just that the key will not remotely lock or unlock the car (same with spare key) and all these systems were still on even after pressing the stop button.

I'm sure its a short circuit somewhere but im at a loss of where to start looking as these cars are not known for these kinds of issues.

Also, if this helps; when i start the car by pressing the start button i hear two distinct 'clunks' or 'clicks' that sounds like its coming from the high voltage Battery underneath the boot. Which was not there before all these issues started.

Any help would be appreciated.

Thanks,

Josh

matt8 · March 17, 2022

Low 12v Battery seems to be the cause of many gremlins.

Worth testing the Battery and replacing it. Or at least giving it a good top up with a trickle charger if it is not too old / defective.

Watch out for killing your radio when disconnecting the 12v and / or switching the 12v for a new one. Documented issue on these forums, very expensive fix.

Herbie · March 17, 2022

I agree with Matt - 12V Battery failing. This can cause all sorts or weird gremlins to appear.

Go to a garage or even car accessory shop like (urgh) Halfords and ask them to load test it. If you put a multimeter across it you may well see 12V but if any load is put on it, that voltage may drop like a stone.

steve2006 · March 17, 2022

I tend to agree regarding the 12V auxiliary Battery, the clunks you hear are the HV contactors being energised and if the 12V Battery is low charge they will not pull in cleanly resulting in excessive arcing across the contacts which can lead to them being stuck.

Faults on these however normally flag a fault code.

Go for the Battery test first as advised and replace if required, it has been mentioned that Lexus were the cheapest source for a replacement so maybe worth contacting Derby Lexus.

agent_dess · March 17, 2022

3 hours ago, matt8 said:

Low 12v battery seems to be the cause of many gremlins.

Worth testing the battery and replacing it. Or at least giving it a good top up with a trickle charger if it is not too old / defective.

Watch out for killing your radio when disconnecting the 12v and / or switching the 12v for a new one. Documented issue on these forums, very expensive fix.

Can you provide the link to the killing the radio when changing Battery?

matt8 · March 17, 2022

11 minutes ago, agent_dess said:

Can you provide the link to the killing the radio when changing battery?

Extensive conversation and developments here.

https://www.lexusownersclub.co.uk/forum/topic/126933-screen-black-after-battery-change/

agent_dess · March 17, 2022

8 minutes ago, matt8 said:

Extensive conversation and developments here.

https://www.lexusownersclub.co.uk/forum/topic/126933-screen-black-after-battery-change/

I remember this thread now

Josh86 · March 17, 2022

Thanks for the quick replies i appreciate it.

So i had a look at the Battery, the date code on it is MAR 2020 so its quite new. I tested the voltage and it was coming up as 12.64v. But i did take it out and put it on a trickle charger for about 7 hours. Unfortunately this doesn't seemed to have helped.

1. The car still thinks its on when its not, and now even stranger; when i put the light switch to fully off (from auto) the daylight running lights still stays on. Before when i did that all lights went off. The climate control stay on also, however the head unit is now turning off.

2. I scanned the car with techstream (on a really bad laptop btw) and it does not show any issues; except for the loss of communication on most modules when i unplugged the Battery before. I think that's the case as all the timestamps for the ''communication errors'' are all at the same time.

I have booked the car in for a check up on monday at lexus. However im still open to any ideas because i know im missing something. I hope its not something drastic as ive just spent a fair bit on 2x new bearings, 2x reconditioned front calipers and some other suspension bits(no fault of the car, i was just an idiot and bent the tie rod by reversing into a bollard, bearings were on the way out also at 72k miles).

ColinBarber · March 17, 2022

Certainly a weird issue. I assume the vehicle hasn't been tampered with, e.g. someone tying to disable the alarm/break in via wiring in the engine bay?

Ignition being on, possibly a problem with the power management ECU or a relay somehow is stuck on.

matt8 · March 18, 2022

14 hours ago, Josh86 said:

I tested the voltage and it was coming up as 12.64v

Is that with it disconnected from the car and off?

What voltage reading do you get when the car is connected and on? Should be 14.4V or so.

Josh86 · March 25, 2022

Yea the car doesn't seem to have been tampered with at all, which was my initial thoughts as well. I'm also inclined to believe its a power module or relay somewhere but that's out of my depth I think (my brain switched off when I read there are two ECU's and two fuse boxes lol).
With regards to the Battery voltage when the car is running it moves a bit between 14.62 and 14.59 but that seems mostly normal.

The car has been at the mechanics since Monday, ive never seen a more bewildered look on the tech's face as I described the issue to him. Definitely not an everyday or common issue I think. He suggested there could be an problem with the physical start/stop button and would take a look at that.

I haven't received any phone calls since I dropped it off and I cant help but feel like its gonna be very expensive to diagnose and fix. Ill keep you updated anyways on the outcome.

corpjones · April 1, 2022

On 3/25/2022 at 12:46 AM, Josh86 said:

Yea the car doesn't seem to have been tampered with at all, which was my initial thoughts as well. I'm also inclined to believe its a power module or relay somewhere but that's out of my depth I think (my brain switched off when I read there are two ECU's and two fuse boxes lol).
With regards to the battery voltage when the car is running it moves a bit between 14.62 and 14.59 but that seems mostly normal.

The car has been at the mechanics since Monday, ive never seen a more bewildered look on the tech's face as I described the issue to him. Definitely not an everyday or common issue I think. He suggested there could be an problem with the physical start/stop button and would take a look at that.

I haven't received any phone calls since I dropped it off and I cant help but feel like its gonna be very expensive to diagnose and fix. Ill keep you updated anyways on the outcome.

Fingers crossed for you, will be interested to know the outcome 🙂

Herbie · April 1, 2022

On 3/25/2022 at 12:46 AM, Josh86 said:

The car has been at the mechanics since Monday

Probably better taking it to a proper auto electrician rather than a mechanic - mechanics for mechanical things, sparks for sparky things.

Josh86 · May 4, 2022

Ok so after 4 weeks of being at the garage the car is back now and working again! Just going to post what happened so it helps other people in the future.

So after I sent the car to the garage, they were looking at changing the start button on the dashboard. Turns out this didn't fix it as the 12v Battery was dead the next day. Then they started pulling fuses to see if it helped. Pulling the ECU 2 (the body control ECU) fuse turned seemed to do the trick and the radio/ac/lights went off. Plugging it back in brought the issue back.

So they phoned me and told me that and quoted me £1050 for that ECU alone :(. They then left the car overnight with the fuse off but this still killed that 12v Battery again, and they were sure that it was something else(even after replacing the ecu with a new part so they put the old one back)

After a few weeks of head-scratching and basically getting nowhere, the car decided to drop a hint of where the issue was by activating the headlight washer and emptying about 3 litres of washer fluid all over the shop floor. This was a bit suspicious so they looked closely at the headlight washer and pump assembly and PRESTO!!! The Ecu controlling the headlight washers(different to the windscreen washer ECU) had basically had a short circuit, and made the washer pump run 24/7, which also burnt out the motor in the pump when it ran dry. Was quoted £700 just for those two parts to fix it(and it was very fishy that they had the parts in shop already) so I just said **** it and they unplugged that whole assembly and the car has been fine since I got it a few days ago. I think I will wipe the headlights clean myself rather than pay £700 for the stupid headlights to get a stupid spray on them.

All in all it was about £500 plus vat for the diagnosis including a new Battery as the 'old' Battery had died being discharged about 10 times during the last 4 weeks. Basically the issue was with the headlight washer ecu and assembly, and im grateful to them for finding it cuz I would not have in a million years thought it would be something so simple yet so frustrating to find.

Anyways, I hope it helps someone out there who comes across this issue in the future, start pulling out fuses and if it is the body control ecu 2 start looking at what is connected to that ecu, especially the headlight washers as Lexus having the parts on their shelf already means its probably a more common issue with these basically bullet proof cars.

Going forward, I think its time for me to sell this car as much as I've loved it. Its appreciated in value quite substantially since I got it and with a baby on the way, I cannot justify spending at least £500 every time ive had an issue with it(like 5 times already). will settle for a cheap Honda until I can come back to Lexus and own my dream car, the LC 500.
Thank you all for your help in trying to find this issue for me and I hope it proves useful to someone in the future 🙂

All the Best,

Josh

corpjones · May 4, 2022

5 hours ago, Josh86 said:

Ok so after 4 weeks of being at the garage the car is back now and working again! Just going to post what happened so it helps other people in the future.

So after I sent the car to the garage, they were looking at changing the start button on the dashboard. Turns out this didn't fix it as the 12v battery was dead the next day. Then they started pulling fuses to see if it helped. Pulling the ECU 2 (the body control ECU) fuse turned seemed to do the trick and the radio/ac/lights went off. Plugging it back in brought the issue back.

So they phoned me and told me that and quoted me £1050 for that ECU alone :(. They then left the car overnight with the fuse off but this still killed that 12v battery again, and they were sure that it was something else(even after replacing the ecu with a new part so they put the old one back)

After a few weeks of head-scratching and basically getting nowhere, the car decided to drop a hint of where the issue was by activating the headlight washer and emptying about 3 litres of washer fluid all over the shop floor. This was a bit suspicious so they looked closely at the headlight washer and pump assembly and PRESTO!!! The Ecu controlling the headlight washers(different to the windscreen washer ECU) had basically had a short circuit, and made the washer pump run 24/7, which also burnt out the motor in the pump when it ran dry. Was quoted £700 just for those two parts to fix it(and it was very fishy that they had the parts in shop already) so I just said **** it and they unplugged that whole assembly and the car has been fine since I got it a few days ago. I think I will wipe the headlights clean myself rather than pay £700 for the stupid headlights to get a stupid spray on them.

All in all it was about £500 plus vat for the diagnosis including a new battery as the 'old' battery had died being discharged about 10 times during the last 4 weeks. Basically the issue was with the headlight washer ecu and assembly, and im grateful to them for finding it cuz I would not have in a million years thought it would be something so simple yet so frustrating to find.

Anyways, I hope it helps someone out there who comes across this issue in the future, start pulling out fuses and if it is the body control ecu 2 start looking at what is connected to that ecu, especially the headlight washers as Lexus having the parts on their shelf already means its probably a more common issue with these basically bullet proof cars.

Going forward, I think its time for me to sell this car as much as I've loved it. Its appreciated in value quite substantially since I got it and with a baby on the way, I cannot justify spending at least £500 every time ive had an issue with it(like 5 times already). will settle for a cheap Honda until I can come back to Lexus and own my dream car, the LC 500.
Thank you all for your help in trying to find this issue for me and I hope it proves useful to someone in the future 🙂

All the Best,

Josh