Battery Drain

[Jden]

I have a 92 LS400. i have something draining the battery. Anybody know if there is a typical problem spot that i could start with?

alternator is good and the battery is a week old.

[jimbostar]

Do you have an alarm on the car? If so, try not turning it on, I had an alarm on a 735IL that would kill the battery in 2-3 days if the car wasn't being used.

Also, Lexus recommends turning off the remote key unlock feature if your not going to use the car for a while.

[silvermate]

first- make sure all of your interior lights are turned off

second- if you have an aftermarket stereo head unit, if the pwr wire isn't hooked up right that will cause it to drain the batter, that happened in my brothers car once.

if you do have an aftermarket stereo try turning the head unit off when you shut the car off.

make sure all of your battery connections are clean and tight.

[jimbostar]

To follow-up on silvermate's thoughts, also check to see if the trunk and underhood lights are turning off properly.

[BlackSC4]

well more specifically, if you have an aftermarket radio or stereo system, check the remote wire. that's where your unit get signals to know when to shut off, it can be loose. amps are notorious for that.

[BlackSC4]

just another thought you may want to know: unless the battery is deep cycled, you might as well return the 1 week old battery and get a new one after fixing the problem. regular batteries arent meant for draining and recharging, it will loose it's life time a lot sooner.

[tansupplyman]

reading one of these reminded me of something: my LS doesn't have an underhood light which I think unusual. Just wonder if it is standard--and if it is, I sure will wonder where it went!!!!!

[90LS400Lexus]

reading one of these reminded me of something: my LS doesn't have an underhood light which I think unusual. Just wonder if it is standard--and if it is, I sure will wonder where it went!!!!!

I do not think mine has a light either. Perhaps they knew that the hood rarely has to be raised on these cars before they bullt them? :D

[jimbostar]

My SC doesn't have a underhood light either, but I thought you LS guys might - either way, I think I'll put one in!

It's true what blackie said about the batteries, regular car batteries build up a film on the plates when left discharged for a while, which inhibits their ability to be recharged. Deep-cycle batteries are made to be drawn all the way down and recharged (also known as Marine battery).

[Jden]

i have the stock radio and changer set up. thats a good thought on the trunk light and hood light. i know the trunk closed button controls the changer's power. is there a way to tell if you find the short? on other cars if the car is off there is no continuity between the positive and ground.(diconnected from battery) same with the ls400?

[Fuller]

I have the same problem with my 07 SC430. After 4 days the battery is dead. Called Lexus corporate they back the dealer who said it was a typical with Lexus since the cars have 25 computers onboard. I'm having a hard time with this explanation. Anyone else?

I have a 92 LS400. i have something draining the battery. Anybody know if there is a typical problem spot that i could start with?

alternator is good and the battery is a week old.

[Threadcutter]

I have a 92 LS400. i have something draining the battery. Anybody know if there is a typical problem spot that i could start with?

alternator is good and the battery is a week old.

J;

Turn everything off, close all doors. If you have a good quality Volt-Ohmmeter that will also measure DC Amperes, remove your positive battery lead and insert the meter leads in series with the positive battery post and the positive battery lead. Set your meter to measure DC Amps and let everything sit for a couple of minutes. With your hood open, make sure everything is turned off, all doors are closed and the under hood lamp is unplugged. Then, look at the meter and write down how many milliAmps (or God forbid, Amps....) of current the car is drawing without doing anything else.

Once you've got that all set up, remove each fuse (one at a time) from the fuse block, look at the meter to see how much the current goes down (drops), make note of it and re-insert that fuse. Repeat that process for every fuse in the fuse block. Upon removal of the fuse for the offending circuit, the current will go way down and that's how you identify which circuit the problem is on.

These problems don't usually "magically" appear all by themselves. Have you or anyone installed any electronics recently? If so, that's probably where to start looking first.

It's Occam's Razor all over again....."All things being equal, the simplest explanation is the most logical". Don't go wildly tearing everything apart. What has changed recently? New parts added or old parts removed?

Why is the battery new? How/why/what led you to be knowledgeable about the condition of your alternator?

Cleaned your Power Steering Rack Solenoid Filter lately? ;)

If not, your new alternator probably has an unplanned, one way trip to the dumpster in it's near future. If that happens, it won't make the trip alone. It will want your (new, soon to be old......) battery to go with it. Alternators like company, working or not.

For those who have been told something along the lines of "that it's normal for the battery to die in 4 days because of the onboard computers".......Bhoosh Whah!......Someone should get slapped for making that asinine statement........

The "quiescent" current (idle current) will be somewhere in the neighborhood of 8 to 20 milliamps of current, PROVIDED that all of the power supplies for the computers (and the computers themselves) are in good working order. The computer(s) in the car are programmed to go to sleep after a certain period of time of inactivity (no, I don't know how long.......but relatively short......like 5, maybe 10 minutes) in order to minimize the drain on the battery. Disabling the keyless remote function makes perfect sense in order to reduce power consumption. 20 milliamps won't kill a battery in 4 days, unless it's already on it's deathbed. I'd suggest the same troubleshooting method above to find that problem as well.

Fuller;

I just re-read your post. An '07?...........I'd make two more phone calls. The first would be to call corporate back and tell them that as soon as I hung up with them, my next call was going to be to the State Attorney General's Office......

You're serious, right?.........You weren't talking to like, Chrysler or GM? Lexus actually told you that? Good Lord, that's Inexcusible..........

[BillyShaft]

For those who have been told something along the lines of "that it's normal for the battery to die in 4 days because of the onboard computers".......Bhoosh Whah!......Someone should get slapped for making that asinine statement........

X2 on this.

Ask them to show you that in writing. If there isn't an official statement from Lexus on their vehicles' draining a battery in a week, the dealer is lying. The RX400h manual specifically addresses our vehicles draining during several weeks of non-use, but we are a different animal than the average Lexus.

[gtolds]

For those who have been told something along the lines of "that it's normal for the battery to die in 4 days because of the onboard computers".......Bhoosh Whah!......Someone should get slapped for making that asinine statement........

X2 on this.

Ask them to show you that in writing. If there isn't an official statement from Lexus on their vehicles' draining a battery in a week, the dealer is lying. The RX400h manual specifically addresses our vehicles draining during several weeks of non-use, but we are a different animal than the average Lexus.

I have heard that some cars have a problem with the seat belt not retracting and that somehow drains the battery. Don't know much more about it but I thought it was interesting...

Maybe a longshot but add it to your list of things to check.

GL

[joelsin]

Do you have an alarm on the car? If so, try not turning it on, I had an alarm on a 735IL that would kill the battery in 2-3 days if the car wasn't being used.

Also, Lexus recommends turning off the remote key unlock feature if your not going to use the car for a while.

Can someone explain exactly how to turn off the remote key unlock feature. My recently acquired 2004 ES330 has a battery that drains on occasion and I can't figure out what is the cause. I have an XM Radio which was added to the vehicle, but is not being used. The other day I changed the air filter and unplugged the connection that connects to the housing. When i tried to start the vehicle the instrument panel indicated a drained battery which was not the case; previously, the battery was starting the vehicle just fine.

[17LexusOwner]

For those who have been told something along the lines of "that it's normal for the battery to die in 4 days because of the onboard computers".......Bhoosh Whah!......Someone should get slapped for making that asinine statement........

X2 on this.

Ask them to show you that in writing. If there isn't an official statement from Lexus on their vehicles' draining a battery in a week, the dealer is lying. The RX400h manual specifically addresses our vehicles draining during several weeks of non-use, but we are a different animal than the average Lexus.

Lexus is the maker of the Car of the WORLD. they wouldn't design a car that would kill it's battery in 4 days. they are not cheap like GM.

Fuller, regarding your '07 SC

Check your parasitic loads. If at all possible (it's a long shot) try and find another car like yours that doesn't lose a charge and see how much parasitic load it has and then compare it to yours.

And also another tip, I would bring it to the Lexus dealer in your area and demand that they find out the problem since I am sure that your car is still under warranty. They are not very good mechanics if they can stare you in the face and tell you that it's because of the computers onboard.....

[inner]

hi,  i am new to this , but i have a similar situation with  my 1999 ls400.    I had parked my car for 3 months and didnt disconnect the battery as i was hoping to start it regularly.  needless to say that didnt happen and my battery died.  i ended up getting a new battery.  shortly after starting to drive it, the engine light came on.  the computer was indicating door was open when it wasnt and then the battery would drain overnight and wouldnt start in the morning.   i havent done any work to it other than change the battery.  also it is showing rear tail light failure, but i think that was doing that before i parked it.   the temperature gauge needle also just drops periodically.  i have been told by my mechanic could be costly fix and might have to put the car to rest.    the mechanic is a friend of mine, so dont think he is lying to me, i dont think he knows exactly what the issue is.   any help. 

[sha4000]

On 1/18/2021 at 4:06 PM, inner said:

hi,  i am new to this , but i have a similar situation with  my 1999 ls400.    I had parked my car for 3 months and didnt disconnect the battery as i was hoping to start it regularly.  needless to say that didnt happen and my battery died.  i ended up getting a new battery.  shortly after starting to drive it, the engine light came on.  the computer was indicating door was open when it wasnt and then the battery would drain overnight and wouldnt start in the morning.   i havent done any work to it other than change the battery.  also it is showing rear tail light failure, but i think that was doing that before i parked it.   the temperature gauge needle also just drops periodically.  i have been told by my mechanic could be costly fix and might have to put the car to rest.    the mechanic is a friend of mine, so dont think he is lying to me, i dont think he knows exactly what the issue is.   any help. 

Take your car to a better mechanic, none of those issues would lead me to believe that your car is ready for the junkyard. I suggest you get a second opinion.

[RX400h]

On 1/18/2021 at 1:06 PM, inner said:

hi,  i am new to this , but i have a similar situation with  my 1999 ls400.    I had parked my car for 3 months and didnt disconnect the battery as i was hoping to start it regularly.  needless to say that didnt happen and my battery died.  i ended up getting a new battery.  shortly after starting to drive it, the engine light came on.  the computer was indicating door was open when it wasnt and then the battery would drain overnight and wouldnt start in the morning.   i havent done any work to it other than change the battery.  also it is showing rear tail light failure, but i think that was doing that before i parked it.   the temperature gauge needle also just drops periodically.  i have been told by my mechanic could be costly fix and might have to put the car to rest.    the mechanic is a friend of mine, so dont think he is lying to me, i dont think he knows exactly what the issue is.   any help. 

Check the cable connections to the battery's terminal posts. An alternator can't charge if the the connections are not good. 
You can also take your vehicle to an auto-electric shop. They solve battery drain issues that dealership mechanics cannot. 

[mikaelse]

Showing door not closed is probably the door sensor.
Will leave light on in door permanently. 
A full good battery should be able to handle that for several days.
 

[Lexus Owners Club]

11 hours ago, mikaelse said:

Showing door not closed is probably the door sensor.
Will leave light on in door permanently. 
A full good battery should be able to handle that for several days.
 

Totally agree, battery drain can be minimal such as interior light being on - don't forget trunk light but you won't be able to see this unless you are inside with the lid closed (bit like the fridge light 🙂

[Isaac elicier]

I just got a 96 ls400 came with a small Honda battery lol. changed it out wit a diehard battery and it worked perfectly till I let it sit for a week then comes to find out that it’s dead. so I used my roommate battery and it starts right up no issues and I was able to take his battery out and put mine back in while the car is running which tells me it not the alternator. And when I got the car the truck latch was broken so that was the first reason why it drained the first battery it came with. I fixed the truck latch and bought the new battery and I thought I fixed the issue. Also when I bought the car the truck looked like somebody tried to pry the truck open so I wonder if the draining problem is coming from the alarm fuse not sure if that accurate just looking for any type of closure or somebody who’s had this issue before. Lights don’t come in when I insert the key I don’t hear a click sound I have to disconnect the battery every time I drive and park it. Please I’ll take any advice. Car only has 113k miles.

[paulo57509]

13 hours ago, Isaac elicier said:

I just got a 96 ls400 came with a small Honda battery lol. changed it out wit a diehard battery and it worked perfectly till I let it sit for a week then comes to find out that it’s dead. so I used my roommate battery and it starts right up no issues and I was able to take his battery out and put mine back in while the car is running which tells me it not the alternator. And when I got the car the truck latch was broken so that was the first reason why it drained the first battery it came with. I fixed the truck latch and bought the new battery and I thought I fixed the issue. Also when I bought the car the truck looked like somebody tried to pry the truck open so I wonder if the draining problem is coming from the alarm fuse not sure if that accurate just looking for any type of closure or somebody who’s had this issue before. Lights don’t come in when I insert the key I don’t hear a click sound I have to disconnect the battery every time I drive and park it. Please I’ll take any advice. Car only has 113k miles.

This is such BAD practice and should never be done.  The battery shorts AC spikes and transients to ground.  Removing the battery while the engine is running allows spikes and transients to run throughout the car's electrical system potentially causing damage to every semiconductor circuit in the car.

At best, this practice can also damage the alternator diodes and voltage regulator.

Electrical damage doesn't happen in every instance this is done.  But now that you're having issues who knows where the fault it.

[Flying Wrenches]

Connect amp meter, pull all fuses and reinsert first one  writing down noted current draw then unplug that fuse (do with key off like your car in shutdown) value., repeat this process till all fuses are checked of current draw   You will find the bugger!

 

Edited May 31, 2022 by Flying Wrenches
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