New LS400 owner, but battery drain issue

JonnyM · December 19, 2016

Hi All,

I've been wanting an LS400 for the last 5 years and picked one up this week. It's a late 1998 series 4 UCF21 with 70k miles, the first 64k with Lexus main dealer stamps and then by independent mechanics over the last 9 years. I'm planning to use it as my main car for long work journeys once I have some things sorted. I've treated it to a Terraclean at Ace Car Care in Shrewsbury - which was a good experience and have serviced it, new plugs etc - purrs like a kitten and a joy to drive. On the second day it failed to start due to a low Battery voltage so not knowing the history of the Battery and wanting a reliability replaced it with a 95 AH Yuasa Silver Battery. The new Battery started it fine but was discharged by the following morning! I've measured the voltage drop across all of the fuses when the car has been off for 10 minutes. There was no voltage across the fuses in the interior fuse box inside. Under the bonnet I measured:

3mV on the MPX-B (multiplex communication system, related to combination meter)
1.9mV on the ETCS (electronic throttle control system)
0.8mV on the OBD
0.8mV on the Dome (MPX and seat control system)
0.4mV on the EFI-2 (transmission)
0.2mV on the EFI-1 (engine)

As it is running up to Christmas I won't get an auto electrician now until early January (not that I'm in a huge hurry). I wondered if anyone had some ideas or previous experience with this on an LS?

I'm planning to fix the parking dings and convert to LPG if she turns out to be reliable in the next 3 months.

Cheers

Jonny

The-Acre · December 20, 2016

A great choice of car, you'll love it!

Assuming the alternator is OK, have you checked that the boot light is going out?

plexus914 · December 20, 2016

Before you measure any rest current your car has to get into "sleep mode". Keep in mind that in order for the car to sleep at all, it must be off
and nothing can be "touched" (no opening of the trunk or doors, no pressing any buttons on the key fob, etc.) If something is touched, the timer starts all over again. How long it takes for it "to go to sleep" I am not quite sure, but 30 minutes should be enough and rest current should be under 0,05Amps (50mA)
For comparison my 1997 LS400 has a rest current of 24,8mA. Alarm went off at about 11,82Volts. Batterie should be charged when less than 12,4Volts (75%).

Procedure of how I did it and got a reading of 24,8mA:

- Turn ignition off and pull the key

- Open engine bonnet and close its lock with a screwdriver

- Close all doors

- leave the Battery connected and arm the anti theft deterrent system either by key or by key fob.....and check
security lamp if it works

- to be sure leave the car alone for about 30 - 60 minutes (I went back to the car after about one hour)

- go back to the car's Battery and measure rest current without interrupting the current.

Before disconnecting the Battery put the pair of test leads (black one/-)to the negative Battery terminal and
the other (red one/+/amps or mA) to the negative terminal clamp.......now disconnect carefully terminal and clamp.

steve2006 · December 20, 2016

Hello Jonny and welcome to the LOC.

With the new Battery discharging so quickly overnight it sounds like a heavy current draw from somewhere, even leaving an interior light on all night is unlikely to completely flatten the Battery.

The best way to determine parasitic current draw is by using a clamp type ammeter on the main Battery lead, from what I remember this should be around 18 - 25mA

You can also use a conventional digital multimeter set to measure current but be aware these generally only measure a maximum of 10 Amps, there are plenty of tutorials for the safe procedure on YouTube.

If your parasitic current draw is well in excess of the normal figure then begin diagnosis by removing individual fuses and rechecking the current draw each time, if it drops to the normal level when a particular fuse is pulled then the circuit the fuse supplies is the one to investigate further.

If removing non of the fuses makes any difference then the alternator could be suspect with a faulty regulator or diode pack or you may have a damaged cable going to earth although the latter is usually obvious by the smoke it produces!

Although unlikely check your boot light is going off when it is closed, at one time this meant someone being shut in there but simply place your camera phone in there on video record mode and then check the playback.

Just out of curiosity were you aware of this problem when you bought the car?

steve2006 · December 20, 2016

Sorry if I've repeated anything Phil and Q, in the time it took me to reply you have both posted as well.

Tinonline · December 20, 2016

This is an infuriating problem and one that I suffered on my Jag S type.

I had all manner of diagnostics and it was put down to an intermittent fault and one that needed more investigation. Mine drained down over a period of two weeks.

The Battery held charge and cold cranked with all the right readings.

The issue? The Battery...an auto elecy noted I had a Lion Battery (a replacement for one that failed in a couple of months) and he had multiple instances with this issue with all looking fine. I swapped it out for a premium brand and voila - issue resolved. Luckily the whole incident cost me the Battery upgrade amount alone thanks to warranty.

...just in case all looks well and you are left wondering what to do next...

Bluesman · December 20, 2016

Hi Jonny and welcome to the LOC, we are a friendly bunch so please dont hold back asking questions big or small should you have any problems with your car. We always welcome ideas on how to overcome problems with our cars but as they are the finest cars in the universe they dont go wrong that often.

I am sorry you are having problems with your Lexus at the moment but I am sure the membership will be very helpful.

You have bought a great car and one that converts well to LPG.

We always love to see pictures of your cars so don't be shy.

Happy Lexus Motoring.

Mike. Bluesman.

Scribe · December 20, 2016

Yes, welcome Jonny. Your car looks great.

As you may have gathered from other threads on here, electrical issues aren't uncommon but often have very simple causes, e.g. weak batteries. In my case it's caused by not using the car much, and is worse at this time of year than in summer. But it sounds like you won't have that problem once the current issue's sorted. Mine is the best long-distance car I've ever had, and I usually get 30+ mpg on a long run.

messi · December 20, 2016

Hi and welcome to the Loc

The Ls400 is probably the best car I have ever had, I now drive an sc430, but the Ls400 is for me still the best Lexus ever made. Regarding the Battery issue, I had the same issue on an Ls400 I had, it was the alternator, went to a company called Foreign Car Spares here in Birmingham, they supplied an fitted one of another ls400 they were breaking for £50, and job done

JonnyM · December 21, 2016

Thanks everyone for all of your responses, I now have a plan! I've got my CTEK charger back from my bother-in-law and am fully charging the Battery overnight. I've received in the post a multimeter with a current clamp. In the light tomorrow I'll put a screwdriver in the bonnet catch to ensure the systems sleep and properly measure the current draw after a few minutes. I'll test the alternator to see if the diodes are leaking - I'm tempted to change out the alternator anyway as I want to do what I can to ensure future reliability. I'll keep you posted on how it's going ...

Colin M · December 22, 2016

I had similar problems to you, Jonny, and it turned out to be the alternator. This was after I had bought a new Battery ...

Well worth checking the alternator out. It turned out to be an intermittent fault on mine - when it was checked initially, there seemed to be no problem with it but on further investigation it was found to be charging only intermittently.

Good luck in getting it sorted.

Tinonline · December 23, 2016

Yep definitely not recommending swapping components out without diagnosing the root cause. That would be a last resort.

i don't believe Lexus suffers from the appalling and often invisible electrical issues that plague the S Type Jag....

Chris Skelton · December 30, 2016

I never set my alarm on my Ser 4 car. But this sounds more serious than my 2-3 week drain hassle.

Strangely, given Citroen's reputation for electric glitches, my XM 3 litre currently seems to be happy sitting unused for several weeks (AND in cold!) without losing too much voltage. (He said, touch wood)

New Year greetings, all.

JonnyM · January 1, 2017

Happy New Year Everyone! Here's a quick update and another question...

I took my LS400 to a local indy to test and replace the alternator. His conclusion was the alternator is fine but the starter motor solenoid is sticking, it's possible this was causing the Battery drain. It makes sense to me as I was getting a single click each time I attempted to start the car when the Battery was fully charged. When the car is asleep (screwdriver in bonnet catch) the drain is only 12mA. Whilst waiting for the parts to arrive I've been using the car daily and since it has started first time every time! I was going to get an exchange starter fitted as the lead time from Lexus is 8 weeks, but now she is behaving I'm thinking that I could wait and get the original Lexus part fitted. Does anyone have a view on whether starting the car up every day might have improved the starter solenoid condition? Before I bought her I expect that she had not been driven regularly for a couple of years which can't be good for a car. I have to say that I'm just loving driving the LS400!

ambermarine · January 1, 2017

The issues with the starter motor are usually linked to Battery status the amperage required to turn the motor is high and although your Battery may look Ok in terms of general use whilst driving and using the car ,the Battery on the LS400 is constantly being used when the car is idle.

I soon found that if I left my car unused for ten days the Battery could just about turn over the engine but unlikely to start it if I left it a fortnight I would get the dreaded click.

I have my car on a intelligent float charger which keeps the Battery topped up and I do not get any electrical gremlins on any of the systems within the car.

It may well be that previous owners of your car let the Battery run down and this could have set a default mode for your starter ,but I think if you keep the Battery at its optimum charge the starter problem will disappear .

Bluesman · January 1, 2017

Having just seen a post on another subject do you know if you have a tracker fitted in your car? Apparently they drain the Battery, could be your answer. Mike.

JonnyM · January 1, 2017

20 minutes ago, Bluesman said:

Having just seen a post on another subject do you know if you have a tracker fitted in your car? Apparently they drain the battery, could be your answer. Mike.

Thanks Mike, I'm not sure whether a tracker has been fitted. When I was checking the fuses a few days back I noticed a retrofitted cable connected to the Battery positive cable. It had an inline fuse which I removed, this may be for the Nokia car kit (if only I'd kept my Nokia 6210 from 2000, the best phone I've had!) or potentially a tracker. Since removing this fuse and driving each day she is starting first time every time. Over the next weeks I'm fitting a Bluetooth phone kit, a Bluetooth and aux input to the stereo and a 'birds eye' parking camera system so I'll have a look out for a tracker whilst I had trim removed. I'll write up the build with photos in case anyone else on the forum is interested.

Bluesman · January 1, 2017

I have a Nokia 6210 in mine. I picked it up on eBay for about £10. Works a dream.

ambermarine · January 2, 2017

Jonny

It is unlikely the retro fitted positive lead was a tracker supply, the concept of a tracker is not to let anyone know the vehicle as one, giving the trackers time to find the vehicle before the stealers find the tracker. The wiring for a tracker is clandenstine and very difficult to find.