RX400h 12V battery drain overnight

stevlee · August 22, 2019

Hi everyone, hoping you can please advise, my RX400h has developed a problem where the 12v Battery is drained overnight. Started a month ago the alarm drained the Battery completely.. my fault, down to like 7v with the multimeter measurement. After trickle charge back to 12.7v Battery was fine for a month. Last week after the rain, I discovered puddle of water on driver side floor. Probably sunroof blocked. I unblocked now, but at the same time discovered 12v Battery is completely drained, measured at 5.3v. Again I trickle charged for 3 days back to 12.7v. After re-charge car goes to READY state and drives ok with no warning lights. Parked up overnight. Next day Battery drained again down to 7v. Not even enough to power interior lights. The Battery is only 1 year old and its a lexus/toyota Battery from the dealer. Any help would be appreciated on direction to solve this.

PCM · August 22, 2019

Door light left on, charger left plugged in ... ?

luckylemon · August 22, 2019

39 minutes ago, PCM said:

Door light left on, charger left plugged in ... ?

Would charger be taking any power without key being in? (I though they should be all off when car is off).

Herbie · August 22, 2019

Good suggestions from Piers above but you also need to check Battery voltage when the car is in READY.

As you may know, our hybrids don't have a traditional alternator and the 12V Battery is charged from the hybrid (traction) Battery via a DC/DC converter, so having the car in READY is our equivalent of the engine running and the alternator spinning. You should get around 14.4 - 14.7. If not, then there's something wrong with the inverter/converter.

stevlee · August 22, 2019

Thanks Piers for reply, door light not on. I have car camera plugged in 12v socket, but my understanding is power is cut to the 12v socket when car is off. 12v Battery is charging again. I will try remove all accessories to re-test. Other mod is Grom audio connected to the stereo, assuming no short circuit from Grom?

stevlee · August 22, 2019

2 minutes ago, Herbie said:

Good suggestions from Piers above but you also need to check battery voltage when the car is in READY.

As you may know, our hybrids don't have a traditional alternator and the 12V battery is charged from the hybrid (traction) battery via a DC/DC converter, so having the car in READY is our equivalent of the engine running and the alternator spinning. You should get around 14.3 - 14.5. If not, then there's something wrong with the inverter/converter.

thanks will do I will check tomorrow once Battery is back to 12.7V in READY state. However if issue with inverter/converter should I not get a check engine light so I can scan with odb2 scanner? Current no check engine light, but I can run Torque pro scan next time when 12v Battery is ready again.

Herbie · August 22, 2019

14 minutes ago, stevlee said:

However if issue with inverter/converter should I not get a check engine light so I can scan with odb2 scanner?

Possibly, I'm not sure.

One thing I do know is that some OBD2 codes are manufacturer-specific so a generic reader is very unlikely to be able to read anything to do with Toyota/Lexus hybrid systems. If you've got a laptop then the best thing is to get a miniVCI cable from eBay, as it will come with a copy of Techstream which is the diagnostic software used in the main dealer workshops.

Of course, it will be a pirated copy so it's up to your own conscience as to whether you use it or not. You can officially and freely download the software from Lexus and then pay for a block of time to use it, but either way you'll need that miniVCI cable anyway. This is the one I got and I can confirm that it works well.

stevlee · August 22, 2019

Purchase

9 minutes ago, Herbie said:

Possibly, I'm not sure.

One thing I do know is that some OBD2 codes are manufacturer-specific so a generic reader is very unlikely to be able to read anything to do with Toyota/Lexus hybrid systems. If you've got a laptop then the best thing is to get a miniVCI cable from eBay, as it will come with a copy of Techstream which is the diagnostic software used in the main dealer workshops.

Of course, it will be a pirated copy so it's up to your own conscience as to whether you use it or not. You can officially and freely download the software from Lexus and then pay for a block of time to use it, but either way you'll need that miniVCI cable anyway. This is the one I got and I can confirm that it works well.

just purchased now thanks Herbs, hope the software don't come in CD format... 🙂 I will also purchase a new 12v Battery to test. Any recommendation? The IS300 Battery is just way too big to fit into RX to test for overnight drainage.

PCM · August 22, 2019

1 hour ago, stevlee said:

Thanks Piers for reply, door light not on. I have car camera plugged in 12v socket, but my understanding is power is cut to the 12v socket when car is off. 12v battery is charging again. I will try remove all accessories to re-test. Other mod is Grom audio connected to the stereo, assuming no short circuit from Grom?

... and also none of those door closed sensors stuck on open?

Herbie · August 22, 2019

35 minutes ago, stevlee said:

just purchased now thanks Herbs, hope the software don't come in CD format

Yes, it is a CD so if your laptop doesn't have an optical disc drive you'll need to get an external one (about £15) or borrow one from someone. The disc is only needed to install the software, not to run it, so once it's installed that's it.

stevlee · August 22, 2019

43 minutes ago, PCM said:

... and also none of those door closed sensors stuck on open?

Thanks Piers for reply, I did keep doors open for like 2 hours with both interior lights to wet/vac the driver side carpet and puling out the driver side plastic skirt to clear the mud/leaves blocking the drain. After this work, the remote alarm was back on to lock doors so I know there is enough power from the 12v Battery at that point. Also the interior lights went off when I keyfob locked the car

Herbie · August 22, 2019

2 hours ago, stevlee said:

I will also purchase a new 12v battery to test

Rather than a new Battery just for testing purposes, why not get a jump start Battery pack like this one instead?

If the Battery is faulty it'll be covered by warranty given that it's only a year old so your money is probably better spent in getting one of these. The 12V batteries in hybrids are small and don't have much capacity so it's not exactly common, but not unheard of either, for people to come back to a flat Battery after a two-week holiday and the car has been stood in the airport car park doing nothing.

These little units are brilliant and work really well. Small enough to sit in the glove box, it's always handy if it's ever needed. It also stops you from looking like an unhelpful scrote if anyone asks you to provide a jump start for them rather than refusing (because you should never use a hybrid to provide a jump start).

Herbie · August 22, 2019

Assuming that the DC/DC converter is working alright and you do get about 14.4 - 14.7V when the car is in the READY state, you'll then have to start looking for the source of the parasitic drain.

The car needs to be in 'sleep mode' for any chance of tracing the fault. This means that you may need to wait for a couple of hours after switching off the ignition and removing the key (and keep the key out of wireless range too). If the doors have pin switches to operate the internal lights you'll need to put a piece of tape over them so that the ECU thinks the doors are shut and the lights don't come on.

Once the car is in sleep mode, a normal quiescent current draw will be about 0.035mA or 35-milliamps. This is to keep the settings of such things as the radio presets, seat memory, alarm, GPS and maybe even more things too. If you find that the current draw is slightly higher, say 0.040mA that may be acceptable for the amount of stuff that needs to be kept alive - maybe Lexus publish figures of what's 'normal' for the car, I don't know?

If, on the other hand, the draw is something like 0.080mA or 0.100mA then something is definitely wrong. As an example, if the car has a 50Ah Battery and a draw of 0.085mA, it would go from fully charged to fully discharged in about three weeks (if my maths are correct :rolleyes1: ).

It used to be acceptable to disconnect the negative Battery clamp and wire an ammeter in series, then measure the draw and pull and replace each fuse in turn until the value dropped and that would be your faulty circuit, but there's a better way to do it now because disconnecting the Battery could reset the ECUs and make the very fault that you're chasing, disappear.

The preferred method now is to switch your multimeter to a millivolt scale (I know that we've been talking Amps up to now but for this you definitely need it on millivolts) and simply put the test probes across each fuse in turn because you're looking for the voltage drop across the fuse. In very general terms, the higher the voltage drop the more current is flowing, so the highest reading should be your faulty circuit. For a more accurate result you can refer to these charts here.

Once you have a circuit that's giving a high reading you can pull that fuse and confirm the actual current draw by switching your meter to the Amps scale and placing the probes into the fuse socket.

There's quite a few good videos on Youtube that demonstrate better than I can describe in words, so just search for videos on 'finding parasitic draws' if you want to.

stevlee · August 27, 2019

Sorry for the late update, was away for the long weekend. Hope you all had a good one.2

12v Battery full re-charged and reinstalled. When car is On running with Ready to drive. I get 14V and when first click of key. I get between 12v and 11.9v. Will check again tomorrow morning to see how much this dropped.

Herbie · August 31, 2019

Any progress on this Steven?

stevlee · August 31, 2019

Thanks Herbie for the follow up. I saw several of the parasitic drain test on youtube. The tests might be beyond my ability sadly... Only update so far is booked car back with Lexus next Wed to have the 12v Battery inspected and hopefully fingers crossed replaced under warranty. Not sure if it is just me been conscientious and starting the car daily (short Battery re-charge) or if the blocked sunroof resulting in soaking driver footwell is related to a short circuit and the parasitic drain. This week the car is bone dry, and so far goes into ready state with around 11.8-12v from the diagnostics screen and started every time / every day since I last posted. The first time the 12v Battery was flat and re-charged, the driver footwell was still soaked and overnight the 12v Battery was drained completely.

ColinBarber · August 31, 2019

less than 12v means the Battery is less than 40% charged. Given the deep discharges the Battery has had it probably needs to be replaced once you resolve the parasitic load issue.