Get your alternator tested. let your car sit with a good battery and if it go dead its a short somewhere or you can start the car and unhook the battery while its running and if its stay on the alternator pretty much good . Trace the wires to the alternator from the battery (do the same with the starter ) and look for wires for cut insulation could be grounded.

 

i have a 1999 es300, same problem. have changed alt about 8 times, still same problem. charges strong for about 15-20 minutes, them as enging idle speed goes down, so does voltage. last alt came from lexus, but same thing. have had alt shops and several mechanics look at it and they cant come up with anything. would love to find answer to this problem. alt charges fine at highway speed, but not in stop and go traffic, or ideling for long periods of time. battery does not run down just by sitting, will start strong after sitting for a week. any ideas???? thanks .

 

PROBLEM SOLVED ... FINALLY!!! apparently it's a common lexus problem (according to my mechanic who's fixed this many times). there's a clip that holds one (not sure which) of the wires coming from the alternator to battery that comes loose. he just resoldered or glued it back in place and voila - problem solved! $48 fix for 1hr labor. the problem isn't a major fix if you really think about it, because there aren't too many components between the alternator and the battery. it's usually ALWAYS the wiring between the two. hope this helps?

 

I'd be interested to know about this "clip " as the alternator feeds straight to the positive bus bar at the side of the fuse box . Don't know of any solder joint in there.
Would be a great find as all Toyota suffer from barely 12 votls at idle.

 

turns out it was the clip from the faulty plug/pigtail that goes into the alternator. guess this is a common lexus problem? unfortunately, lexus doesn't sell a replacement harness and tries to bully you into buying the entire engine compartment harness for $1800. however, after some digging ... i came across a replacement plug (both the round and rectangular) for "nippondenso" alternators on ebay for around $20 that fits perfectly. the "glue" job my mechanic did only lasted about a week. he did warn me that it was just a temporary fix though. none of the salvage yards in my area had (or maybe just didn't want to cut ) the harness i needed.

hope this helps ... I LOVE eBAY and CL!!!

 

Wow, $20 for a little electrical connector, damn. That's what's good about the "pick and pull" junkyards. That connector is a pocket item, or it will cost a dollar if ya really want to pay for it. I got mine for free when I bought my alt for $25, I just had them cut the wire a foot away from the end and told them "Don't take the plug off, just cut it long."
Well, at least you got it, and that must be a common problem b/c mine fell apart also. But it could have had something to do with all the PS fluid leaking on it, maybe that just loosens everything.

 

Glad some of you have found your problem. had my 99 es in a shop for three days, they tried everything i had already done, and had no luck,either. this past saturday i went to Parkplace Lexus in dallas and they put it on thier scanner, had a tech go over it. After about an hour and half, they came in and said everything checks out, we dont know what to tell you. it should be working. They dint charge me anything, but still dont know whymy alt doesnt keep the battery charged. Oh, well, guess i will keep my jumpstarter in the trunk untill i have something else to try. thanks for the input here.

 

i would definitely check that little plug that goes into the alternator ... seems to always be the culprit..

 

well, what can ya do? junkyards wouldn't come off the plug. plus, i'd rather have a new one. that way i know i'm getting something with no issues or prior wear & tear. i wonder if anyone has thought to construct some sort of shield of some sort to keep the p/s fluid from leaking onto the alternator? i thought about trying. i've gotta crawl up under the car today anyway ... gonna see how hard of a task it may be.

i'll keep ya posted!

 

There's a thread on here somewhere, I'll try to find it for ya. The guy used a bleach bottle cut to cover the alternator, looked pretty good.

Post #2 has a pic of the alternator wrapped with a bleach bottle; https://www.clublexus.com/forums/ls4...lternator.html

 

that's a pretty cool idea. hmmm ... bleach bottles to fix the alternator short problem, a milk container lid to fix the tilt steering issue. boy, us lexus owners sure are creative, aren't we? since i have to scrape all this gunk off that my mechanic caked on trying to hold the plug in place, i might as well construct my "bleach bottle shield" and i think i'll coat my plug with silicone when i install it to give it some added protection against the elements and fluids.

 

Yeah it's amazing how some little pieces of plastic fix some of the stuff that millions of dollars of engineering came up with. I wrapped the alt. plug with electrical tape and used zipties to hold it in place so it doesn't get broke or pull the wires out again. Ya work on cars long enough and ya come up with great ideas that the engineers wouldn't even think about. And they get all the money.

 

it's not a fix, it's a jury-rig so you have time to fix the pump/hose.

the "fix" is to fix the leak lol.

 

as far as i know, mine isnt leaking (no signs of any leaks/alternator is bone dry), but im gonna put the shield on anyway since this seems to be a common problem. "preventative maintenance" ... lol.