My 93LS400 has developed a new problem.
The headlights dim at low rpms. However as soon as u hit the gas and the rpm needle rises, the headlights are bright again.
Any ideas ?
I had the dealer check the Alternator/ battery and it seems to check out fine givingout 14.1 volts when running. Or is it that the tech doesn't really know how to check the alternator and is giving me false feedback ?

 

Hmm, it sounds like it is definitely an alternator problem. Did they measure the voltage when the car was at idle? I'd suggest you have the dealer (another techician) double-check it again.

 

I have the same problem with my car. It doesn't seem like a big problem to me, so I'm not worrying about it.

 

I'm having the same problem and I thought it was the battery, are you suggesting that the alternator is failing?

 

The dealer checked the alternator again since i insisted it had to be the case. Turns out the alternator was dropping voltage from 14.1 to around 12.3 when the car was at idle for about 15 mins and the rpm needle dropped below the 1 mark.
Initially the tech had checked the output right after starting up the car, at that point the rpm is always high since the car is warming up. usually after 15 or so mins the lexus seems to drop the rpm dramatically to around 0.7 which is what normal readout should be.
It's funny how i had to dictate the procedure this process to the tech in order to pin point the alternator low voltage problem.
Lexus techs sure arent where they are supposed to be.
However I have to mention that the service representatives are the most helpful I've ever found at any dealership. If it wasnt for the service reps I would never go to the lexus dealership for any technical work at all.
At this point I'm getting the alternator changed.
Let's see how that helps aid the dimming headlight situation.
Thanks for everyone's help once again. (especially LS400's).

 

Had the same problem on my 90 LS, when I woud hit the brakes I could see the headlamps dim and hear the a/c blower slow down as well. It was a bad alternator, got a rebuilt unit by Delco (yeah GM!!) for $180 from my local parts house. It had been doing that for years and now the problem is gone. Also put in some Xenon lamps, much better!

Chas

 

Well , just picked up the car from the dealership. They've changed the alternator and put a remanufactured one in for around $450.
Here's the sitution now, this one's worse than the original. My original alternator was giving dim headlights, where as this reman one does the same and to top it, it dims the lights every time the break pedal is pressed.
is this messed up or what ?
what should i do now ? I'll def call the dealership tomorrow, but till i'll need some pointers to give them.
thanks again. !

 

I'm having the same problem with my alternator. Can it just fail on me? How much longer wil it last?

 

I've got a 93 with 75Kmi. on it. When I brake, my lights dim slightly, but within 1 sec., they come back up to full brightness - the car makes the adjustment.

My battery is new within 5 mo's. I've had the car for 2 years and 20K mi. and its always done this.

My blower fan does the same thing. I had a non-Lex tech check it out and he says alt is putting out too little current. My EE degree and personal experience seems to make me think that the alt varies its output with load to maximize mpg. If thats the case, in '93 that would be forward thinking.

Ask the service guy if the alternator varies its output with electrical load.

 

I have seen vehicles with your problem.And it turned out to be the battery.It does not matter how old the battry is,it can still cause your problem.If you have acess to another battery,give it a try and report back and let us know what happened

 

Rybikowsky is right, It's the BATTERY not the alternator guys.

 

My understanding is that the battery is in passive mode while the engine is running, and that it's the alternator providing the voltage/current at that point. The battery is actually being charged. Therefore I'm skeptical as to why a different battery would cure the situation when it's not acting as the supplier when the engine is running ?

 

I agree with lexs400, the battery doesn't do much but just sit there and get a charge when the vehicle is running.

Chas

 

One of the first things I'd do before replacing the alternator would be to change the brushes. If they are anything like my Supra, they should be around $15 for the kit and are relatively easy to install. I usually change the brushes every 60k miles and I had 137,000 mi. on the Supra when I sold it. I never had to change the alternator. New brushes for my LS400 and SC300 are in my plans.

 

How do you change the brushes?