Headlights dim when brake pedal pressed...anyone else?

[Antman]

Just out of curiosity antman, (couple things to check):

With the key turned 'off', you've already documented your electrical status. But what happens when you do the exact same test with the engine 'off' (lights on...etc ), but w/ the key in the 'on position'; main electrical relay closed and all circuits are live? Is there still a substantial voltage drop?


Also... do that test again with the engine running and you stepping on the brake pedal, but this time, disconnect the brake light switch; just trying to isolate the problem to one system or the other.

[MENTION=83083]rigtec[/MENTION]

Results from your suggestions:

*Key "on" engine off lights DO NOT dim. (no change)

*Disconnected plug at brake pedal- verified that the brake lights were not working- lights still dim while truck is running/brake pressed (no change)

op2:

 

[rigtec]

[MENTION=83083]rigtec[/MENTION]

Results from your suggestions:

*Key "on" engine off lights DO NOT dim. (no change)

*Disconnected plug at brake pedal- verified that the brake lights were not working- lights still dim while truck is running/brake pressed (no change)

op2:

(^^^LOL!) Ahhh, "That's Good"! So now we know/proved that the lighting circuit (brake light switch, harnesses and bulbs) are fine and have nothing to do with this symptom. We also know that the alternator has nothing to do w/ this cuz the problem still exsists with the engine/charging system removed from the equation!

"So now what"...

 

[Antman]

We also know that the alternator has nothing to do w/ this cuz the problem still exsists with the engine/charging system removed from the equation!

That's not correct- the lights do not dim unless the engine is running, no matter what..

 

[phillyd2]

Guess you can stop making fun of me for never using my breaks.

 

[rigtec]

That's not correct- the lights do not dim unless the engine is running, no matter what..

Hummm!? I see....

 

[rigtec]

[MENTION=65614]Antman[/MENTION],

What else in the electrical system 'Loads-up' when you step on the brake pedal e.g., VSC, anti skid, ABS, A-trac, SRS, etc. This is weird, I've never noticed my headlights dimming or any type of 'voltage sag' from just stepping on the brake pedal; this is a first!

 

[Antman]

[MENTION=65614]Antman[/MENTION],

What else in the electrical system 'Loads-up' when you step on the brake pedal e.g., VSC, anti skid, ABS, A-trac, SRS, etc. This is weird, I've never noticed my headlights dimming or any type of 'voltage sag' from just stepping on the brake pedal; this is a first!

Got me?! That's why I started this thread, lol.

 

[1engineer]

He mentioned rolling up a window that's already rolled up and doing the same thing. Its a load issue not a brake load issue. [MENTION=83083]rigtec[/MENTION] FWIW mine does it too wit the window and a map light.

 

[rigtec]

He mentioned rolling up a window that's already rolled up and doing the same thing. Its a load issue not a brake load issue. [MENTION=83083]rigtec[/MENTION] FWIW mine does it too wit the window and a map light.

The window I can understand cuz that's a legitimate load (or momentary 'overload'; as the case may be). But there's also an indication of a difficult load being imposed on his electrical system when the brakes are being applied. Based on the behavior of this problem, I still believe that it's likely a shunted or short circuit. BTW: No shortage of accessories that have been added to this truck either rolleyes: ...just sayin')! Haha! Guess we'll have to start to disable ("Un-plug") each potential electrical draw from this truck... 'one-by-one' until the guilty party is exposed. "Seek and ye shall find"! Regards!

 

[jrandom]

Maybe a bad ground somewhere? Maybe an extra ground cable from battery to frame? (for kicks and giggles)

 

[gm350reratliff]

The window I can understand cuz that's a legitimate load (or momentary 'overload'; as the case may be). But there's also an indication of a difficult load being imposed on his electrical system when the brakes are being applied. Based on the behavior of this problem, I still believe that it's likely a shunted or short circuit. BTW: No shortage of accessories that have been added to this truck either rolleyes: ...just sayin')! Haha! Guess we'll have to start to disable ("Un-plug") each potential electrical draw from this truck... 'one-by-one' until the guilty party is exposed. "Seek and ye shall find"! Regards!

You could try fuses 32 and 33 which are labeled "ABS 1 and ABS 2". Fuse No. 32 is a 50 amp fuse, fuse No. 33 is a 30 amp fuse. I believe one of these is for the brake booster. 30 amps is enough to make the lights dim somewhat.

BTW, I'm not sure if you will trigger any codes by doing this. I claim no responsibility.

 

[LXRunner]

That's not correct- the lights do not dim unless the engine is running, no matter what..

Any one remember about a belt, as a part of that system ?

If system takes more power, it applies more force on the alternator and throw pulleys and belt on the engine. And for a short time at that point, belt may loose traction (you will see voltage drop), then it picks up traction and applies that force on engine ( you may see RPM drop down).

 

[rigtec]

You could try fuses 32 and 33 which are labeled "ABS 1 and ABS 2". Fuse No. 32 is a 50 amp fuse, fuse No. 33 is a 30 amp fuse. I believe one of these is for the brake booster. 30 amps is enough to make the lights dim somewhat. BTW, I'm not sure if you will trigger any codes by doing this. I claim no responsibility.

Hi gm'

This is where it gets tricky; trying to disable potential problem (branch) circuits for testing, but not knowing exactly how the main (source) circuitry is supposed to behave or, will be affected w/o them. Here's where common sense 'SHOULD' come in handy. Rather than defeat any 'DDC' or firmware control modules e.g., ECU's or PCM's etc, perhaps [MENTION=65614]Antman[/MENTION] can (one-by-one), disable a few secondary (analog) relevant devices such as, 'the brake booster' (as you suggested), motorized actuators, electric servos, resistance heaters etc... that may operate when the brakes are initiated; knowing exactly which ones though could get complicated!

PS: With this part of the test, I would avoid pulling the fuses to disable devices because we only want to kill the hardware (like motors), this way we know exactly what will not work; and the circuit can remain active. As you have already mentioned, there may be certain trouble codes triggered as a result of these tests. Maybe someone familiar with Toyota's sophisticated powertrain algorithms like [MENTION=66389]BlackWorksInc[/MENTION] could chime in on this one to impart some insight(?)! "GOOD LUCK!" Lol!

"Now it's my turn"... op2:

 

[Cheers!]

my 2003 subaru legacy GT did the exact same thing your 4runner did. It did it brand new from the factory. Also almost all subarus exhibit this (even STi). I lived with it for 11 years with no issues until I sold her and moved California.

It did this with a stock Subaru battery and also did the same with an Optima RedTop.

 

[gm350reratliff]

[MENTION=65614]Antman[/MENTION]- maybe post a video of your 4runner doing this so we have something to compare to.

I just tested this on my '14 in a dimly lit garage. There is a slight, momentary dimming of the headlights. Almost like a slow blink, if you will. In less than perfect test conditions, I had to look real hard to see it. I forgot to check my 4th gen last night to see if it did it. My 4th gen still has the OEM battery that I suspect is getting a little weak. So it should be more evident on that 4runner. Even if they both do this, I'm not to worried about it as I'm pretty sure it just the nature of the beast.

As for why you didn't notice it before, could be as simple as your mind wasn't looking for it or with age/miles, the brake booster is requiring more amperage than it previously did.

I would possibly consider hooking up a Toyota scanner to see if you could see anything else being triggered.

 

[Antman]

my 2003 subaru legacy GT did the exact same thing your 4runner did. It did it brand new from the factory. Also almost all subarus exhibit this (even STi). I lived with it for 11 years with no issues until I sold her and moved California.

It did this with a stock Subaru battery and also did the same with an Optima RedTop.

Funny you mentioned that. I have been doing research on this all over the web and pulled up exactly what you are talking about several times from Subaru owners/forums. It just bothers me that it just started happening...

[MENTION=65614]Antman[/MENTION]- maybe post a video of your 4runner doing this so we have something to compare to.

I just tested this on my '14 in a dimly lit garage. There is a slight, momentary dimming of the headlights. Almost like a slow blink, if you will. In less than perfect test conditions, I had to look real hard to see it. I forgot to check my 4th gen last night to see if it did it. My 4th gen still has the OEM battery that I suspect is getting a little weak. So it should be more evident on that 4runner. Even if they both do this, I'm not to worried about it as I'm pretty sure it just the nature of the beast.

As for why you didn't notice it before, could be as simple as your mind wasn't looking for it or with age/miles, the brake booster is requiring more amperage than it previously did.

I would possibly consider hooking up a Toyota scanner to see if you could see anything else being triggered.

I can barely post pictures that aren't mildly offensive, a video would probably crash the site :boom:

I am 100% certain this wasn't like this before- I drive to work in the dark every morning and pay attention to stuff like that- it's just the way I am, lol.
I do wonder how many others have this issue and don't hardly notice.

Me- it's driving me nutso.

Could be something to do with age/miles though- I still like your suggestion of a non-100% battery. I think that's possible...

 

[adam2562]

so to clarify.... some trucks came with a 100amp alternator and some came with a 130amp alt? what denotes the difference?

 

[Antman]

so to clarify.... some trucks came with a 100amp alternator and some came with a 130amp alt? what denotes the difference?

That is correct. I don't think anyone- to date- has figured out exactly what determines what you get. I think all Trails and LE's get the 130a- but only some SR5's do.

I thought I would have gotten the 130a with heated leather seats but I have 100a...

You can see the numbers through the drivers wheel well- remove the rubber flap and squeeze in there to see the alternator.


Part Number Description
27060-31190 Alt.- 4.0 L, 130A
27060-31180 Alt.- 4.0 L, 100A

 

[adam2562]

That is correct. I don't think anyone- to date- has figured out exactly what determines what you get. I think all Trails and LE's get the 130a- but only some SR5's do.

I thought I would have gotten the 130a with heated leather seats but I have 100a...

You can see the numbers through the drivers wheel well- remove the rubber flap and squeeze in there to see the alternator.


Part Number Description
27060-31190 Alt.- 4.0 L, 130A
27060-31180 Alt.- 4.0 L, 100A

i would bet that the sr5 premiums get it to aid with the extra stuff like heated seats and turn signals in mirrors and nav possibly.. everyone check your sr5's and sr5 premiums :whip:

 

[jrandom]

You can see the numbers through the drivers wheel well- remove the rubber flap and squeeze in there to see the alternator.


Part Number Description
27060-31190 Alt.- 4.0 L, 130A
27060-31180 Alt.- 4.0 L, 100A

Or just move your phone in from above and snap a pic

I would guess that it is more about which ones come with the bigger power inverters.