Headlights dim when brakes are applied - **SOLVED**

[westwind77]

I have noticed that occasionally the headlights will dim then brighten when I apply the brakes. It does not happen all the time, but at times if I have not used them in 5+ minutes. I noticed subsequent presses of the brake will not cause them to dim. I started to noticed this a few months ago. The 'issue' has not gotten any worse - just consistent. I live in a dark area, so it is easy to notice even the faintest change. They do not dim to where it is a safety concern, just something that is minor but noticeable to myself, the owner of the vehicle for the past 8 years.

Has anyone heard or had this happen on their 4R?

A new battery was installed by Toyota a year or two ago (I have yet to check to see if the connections are tight though, will look tomorrow).

To me it is a power draw / amps dropping that is causing this, but why? Failing alternator?

Just looking for some ideas - just do not want this to get worse on a road trip in the winter or be an early sign of a part failing for a potential break down.

Thanks!

 

[1jzgte]

I have noticed that occasionally the headlights will dim then brighten when I apply the brakes. It does not happen all the time, but at times if I have not used them in 5+ minutes. I noticed subsequent presses of the brake will not cause them to dim. I started to noticed this a few months ago. The 'issue' has not gotten any worse - just consistent. I live in a dark area, so it is easy to notice even the faintest change. They do not dim to where it is a safety concern, just something that is minor but noticeable to myself, the owner of the vehicle for the past 8 years.

Has anyone heard or had this happen on their 4R?

A new battery was installed by Toyota a year or two ago (I have yet to check to see if the connections are tight though, will look tomorrow).

To me it is a power draw / amps dropping that is causing this, but why? Failing alternator?

Just looking for some ideas - just do not want this to get worse on a road trip in the winter or be an early sign of a part failing for a potential break down.

Thanks!

Sounds like a failing alternator. Don't see a high powered stereo system on your mods list but if you have powerful amps and stereo it'll wear out your alternator prematurely if not set up properly.

 

[nglayton]

I noticed on mine when I hit the brakes that the radio lights, knob lights and all the other non-instrument cluster lights dim. It's not the alternator, as I have a new DC Power XP-270 installed and it's not the battery either as it is also new.

However I have never noticed the headlights dimming. I'll have to check that.

 

[westwind77]

So I took the connections off the battery and cleaned both where it clamps the battery as well as the plate connections prior, basically everything is perfect from the battery to the main cables now. I put the front half into the garage when I got home and applied the brakes....the dimming is still there....see the video here:

https://youtu.be/gUH1BALiyd4

You can see the dimming easily. I did notice that the dimming would occur not on the 1st press of the brake, but if I lightened up then pressed down for a 2nd time they would dim. It would happen every time.

Could there be something wrong with a component in the brake system drawing too much power?

*I just looked and they installed a Toyota TrueStart Battery with 575 CCA / 130 RC - That sounds 'weak' to me from what I personally run in my other equipment - thoughts?

 

[83Mule]

Lights are run off the battery....and yes 575 sounds too weak for a 4Runner. You could have a short in the brake wiring sucking juice when you apply. 800 sounds right for the battery.

 

[Antman]

I discussed this a few years back because mine does it. I have had 2 different alternators (upgraded to a Trail alt). and it still happens. There is a pump in the brake booster that must draw a ton of power, that causes the lights to dim.
Don't worry about it! I have 140k almost and all is good.

 

[Jeremy556]

Pretty certain it is the brake booster. Have a look at all of those large wires going into it and the (at least) 130amps worth of circuits in the main fuse box for it.

FWIW, I'm at 200K miles on the original alternator, and my lights have always dimmed every few presses of the brake pedal, since brand new.

ETA: Beat by Antman while I was looking at my fuse box cover

 

[westwind77]

I feel somewhat better (maybe) that others have had this 'issue'. I guess for me is that mine has never done it until recently, so why now? I cleaned the short ground wire going to the side of the truck with no change as well. I have a radar detector with a voltage readout and it will drop almost 1.0v if you press the brakes down hard. That booster sucks some juice!

I have an Exide Edge Flate-Plate AGM battery being dropped off by one of my distributors tomorrow to swap out the one Toyota put in recently, hopefully that helps. If not, oh well, I have a better battery and will live with the dimming and cross my fingers it does not mean anything else!

AGM auto / car battery / automotive battery / truck battery / SUV battery

 

[zerowkul98]

I discussed this a few years back because mine does it. I have had 2 different alternators (upgraded to a Trail alt). and it still happens. There is a pump in the brake booster that must draw a ton of power, that causes the lights to dim.
Don't worry about it! I have 140k almost and all is good.

I remember my 2003 and 2008 Sport Editions did this as well, when the brake booster would kick in.

So, the Trail models have a bigger alternators? Am i getting that correct from the earlier post?

 

[jrandom]

Hah I was going to mention [MENTION=65614]Antman[/MENTION]s thread. Mine do it too, I think most do, people just don’t notice it.

 

[SodiumFlouride]

At first I thought the OP's question was crazy because the brakes don't need much juice, but the explanation here makes sense. Thanks!

 

[PK930]

My '12 SR5 started doing the same thing not too long ago, slightly irritating. Then the positive terminal would get all crusty and sometimes wouldn't start. Cleaned them off pretty good but couple weeks later it started to happen again.

Junked the Panasonic battery and tossed out those crappy sheet metal battery clamps for some marine grade ones. Took some 220 grit paper to the wire ends o the positive cable.

None of that has happened again.

 

[nglayton]

So, the Trail models have a bigger alternators? Am i getting that correct from the earlier post?

100amp vs 130amp. Not sure which models had the 100amp, I know my 2011 Trail had the 130a until I swapped it out for a DC Power XP-270. :flame:

 

[westwind77]

My '12 SR5 started doing the same thing not too long ago, slightly irritating. Then the positive terminal would get all crusty and sometimes wouldn't start. Cleaned them off pretty good but couple weeks later it started to happen again.

Junked the Panasonic battery and tossed out those crappy sheet metal battery clamps for some marine grade ones. Took some 220 grit paper to the wire ends o the positive cable.

None of that has happened again.

I cleaned every connection I could perfectly. I have a couple good friends who are techs and without bothering them too much they say the initial hit for power gets pulled from the battery, then the alternator will kick in more if needed to compensate for any drop, hence the drop and quick re-brighten of the lights. I am a hoping the better battery (to be installed today) can handle the pull of the brakes better without the voltage drop causing the lights to dim. I'll report back after the swap.

 

[Antman]

100amp vs 130amp. Not sure which models had the 100amp, I know my 2011 Trail had the 130a until I swapped it out for a DC Power XP-270. :flame:

100a was for SR5's only- and I think they changed that in 2013. Not positive tho

 

[westwind77]

***Update*** Problem solved!

New AGM battery installed (link in previous post) headlights no longer dim with brakes applied - tested it numerous times in the garage today and this evening.