Headlights Get Brighter When Revving Engine In Park/neutral

[amcdonal86]

Hi,

I just purchased a '97 Coach Edition with 91k miles. I noticed today while driving at night that the backlighting for the climate control kind of dims and brightens very slightly (and randomly). However, I also noticed that when I rev the engine in neutral with the headlights on, they get significantly brighter. Could this be an indication of a bad battery or a bad alternator? Or is this normal behavior?

I appreciate any advice/help! Thanks!

[90LS400Lexus]

I think it depends on the electrical load the car is under and the battery condition. I think my car does this to an extent if most all power accessories are in use.

[landar]

You really need to put a voltmeter on the battery and record the voltage under the various conditions that you mentioned.

It is not uncommon for the voltage to fluctuate slightly. We would have to see your actual readings rather than relying on subjective

observations to know if there truly is a problem.

Remove and clean your battery terminals and cables first before taking any measurements.

[amcdonal86]

You really need to put a voltmeter on the battery and record the voltage under the various conditions that you mentioned.

It is not uncommon for the voltage to fluctuate slightly. We would have to see your actual readings rather than relying on subjective

observations to know if there truly is a problem.

Remove and clean your battery terminals and cables first before taking any measurements.

I will try to get those readings. I don't have a voltmeter, but I will say that the battery looks brand new. The independent dealership I bought it from probably replaced the battery just before selling it to me as the terminals have absolutely no corrosion and the battery itself is very glossy and shiny!

[jcrome04]

It's the alternator.

[ED.]

It could be a voltage regulator but may be the alternator as well. VR is cheaper. A guy from my BMW board said his car was doing that very slightly so he took it to AutoZone and had it (alternator) tested and the guy said it was on it's way out. He then had it bench tested and said it was charging fine so he put it back in with a new VR and still the same! He said it's been six months and no probelms.

He believes that something inside. One of the internal diodes isn't working 100% so it's causing those fluctuations.

I notice that a lot on the LS. Especially with the headlights. My BMW I sometimes see the interior lights flicker ever so slightly with the car running and one of he doors open. I really only notice it on both cars at night.

We had a 2008 Ram for a loaner last week and I was driving it around to move some stuff and I noticed with 30,000 miles the headlights would sometimes dim when you'd hit the brakes. I don't think that was right but not much I could do I guess!

[amcdonal86]

Thanks for all the replies.

Unfortunately I sprained my right ankle on a drunken new years eve rampage so I can't drive the car anywhere. (Actually, my girlfriend drove me around in my LS400 and I felt like royalty sitting in the back seat!!!) As soon as I can drive anywhere, I will take it to advance auto parts and see if the alternator is bad.

Something tells me that nothing is wrong and that I'm just being silly. I haven't noticed it the last few days, but then again I haven't been thinking about it.

[90LS400Lexus]

I dont think my lights dim, but if I have the lights on and the HVAC blower on high, sometimes the blower will speed up when I accelerate. I think my other LS was the same way, as have many cars I have owned in the past. I do not think there is cause to be alarmed yet.

Sorry to hear about your ankles.

[amcdonal86]

Well, I just took the LS out for a spin in spite of my doctor's advice. I did not notice the same issues, even with all of the accessories on. Actually, the backlighting for the climate control still seems to dim a little bit randomly, but it's barely noticeable and there is no correlation to that and the alternator.

I think I will let this slide for now and if I'm feeling really anal later on, maybe I'll try to solve the problem.

For now, I'm perfectly content trying to find a new cabin air filter (currently I'm not running with one because it was filthy and deteriorating).