Noticeable Voltage Fluctuations Normal?

K

KP Texan

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Just replaced the 4 year old battery in my 2012 since it wouldn't hold a charge, and I've been watching the voltmeter much more closely over the past few days. Voltage seems to be normal and stays fairly steady (14.0 volts or so after I start driving, and then settling to around 13.9 volts).

The only exception to this is when I step on the brakes sometimes. I'm not sure how much my voltage drops so I need to put a multimeter on it, but there's a definite movement of the voltmeter needle on the dash when I do. It's not every time I brake, just the first time after not braking for a bit of time.

I've read the electric brake booster draws a lot of power, but I was just wondering if any of you guys have noticed the same thing? I'm just hoping it's normal, and not a sign my alternator is failing!
 
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my 2012 is on the second battery and I get slight quick dimming on braking and on electric window when it hits max up. Would have to say normal as I'm at 182,000. Also, my voltmeter sits slightly left of center most of the time, moves a little with AC on.

If you look into getting into the radio service menu, there is a page in there that will show real time voltage! I think you hold the settings button down and turn your lights on and off 3 times to get in there. Just search the forum, you'll find it.

Also, important, check your terminal connections!!!! My wifes camry corroded so bad it threw up codes and the CEL.
 
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Thanks guys! I'm pretty sure what I'm experiencing is normal - I haven't really even noticed my lights dimming, it's just that dip in the voltmeter needle that had me concerned.
[MENTION=150567]Old Red[/MENTION], it didn't even occur to me that the 2014+ guys don't have voltmeters in the dash (should've known this since I had a 2018). That may be the reason I haven't gotten many responses to this thread! As for my battery replacement, I'm hoping that because it was 4 years old and it had been drained down completely several times, it was just at the end of its life. For future reference, if your kids jump in the back hatch area of the 4Runner, make sure they don't turn the hatch light switches to on!

All of this being said, I think I'm going to run it up to a place that will do free alternator testing just to to rule it out and give me peace of mind.
 
As another reference point: I have Scangauge II and Voltage will vary between 13.4 to 14.1- I see lower reading when it is hot outside and higher reading when it is cold, I am still on my original OEM (Panasonic) battery, it is 6 years old now.
 
Thanks everyone! Just ran out and did some testing with the service menu [MENTION=85141]Jivewalker[/MENTION] mentioned. It looks like the voltage might drop to 13.8V or so for a split second when pressing the brake, or about a .5V change.

Engine Off, A/C on:
kcbshAq.jpg


Engine On, A/C, Headlights on:
bWy8Lcb.jpg


GIF of the voltmeter and service menu readout when pressing brake sometimes:

aJ2Uvz7.gif


hpCAmzK.gif
 
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Service menu is handy, isn't it! You might also consider replacing your brake lamp bulbs or at least unplugging them and then testing, the lamps or harness connections could be your culprit if they are shorting. My gauge does not dip like that, makes me think short or bad connection.
 
Old Red said:
[MENTION=42864]KP Texan[/MENTION], At least you have a voltmeter...

Dimming headlights (after a new battery) plus the other dead battery might be the alternator starting to go. If it can't supply enough juice to charge the battery, and the draw of the headlights while braking causes a drop in light output as the engine RPMs go down, I would think maybe it is the alternator.

I just don't know what the reliability is with the OEM alternator. I know they last quite a long time, but don't know the track record personally.

Anyone know?
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Limited experience here.

My 1988 left us at 305k miles with the original alternator. I had replaced brushes once as a preventive measure.
My 2001 had the brushes wear completely down at about 240k, had to replace the alternator because nobody carries brushes. I knew better...
Note: I have a 2006 Scion at 215k and a 2009 Corolla at 200k. Replaced brushes in both in the past few months, and they really needed it. I heartily recommend replacing brushes at 200k. It's the most frequent cause for alternator failure, I believe.
 
Jivewalker said:
Service menu is handy, isn't it! You might also consider replacing your brake lamp bulbs or at least unplugging them and then testing, the lamps or harness connections could be your culprit if they are shorting. My gauge does not dip like that, makes me think short or bad connection.
Click to expand...

Well, that's a bit unnerving to hear (just remember it's a gif so its playing over and over - the dip only happens once while braking). I'll check out the bulbs and any grounds also just to make sure those are good to go. I hate things like this that may or may not be a problem - I'd almost rather deal with something going out completely than wondering!

[MENTION=83083]rigtec[/MENTION] mentioned "voltage droop" in one of his posts comparing his new high current alternator compared to the stock one. Maybe this is one of the symptoms he's referring to?
 
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mike5 said:
Mine will drop from 13.8 to around 13.3 when braking initially. I see the needle move as well.
Click to expand...

Thanks! Nice to have another data point leaning towards the “normal” side. I honestly think most people don’t notice it because most owners don’t have a voltmeter! I was looking at gauge clusters online, and I think the only ones with it are ‘10-‘13 LEs and TEs. The SR5 in those years did not come with it from what I can tell.
 
KP Texan said:
Thanks! Nice to have another data point leaning towards the “normal” side. I honestly think most people don’t notice it because most owners don’t have a voltmeter! I was looking at gauge clusters online, and I think the only ones with it are ‘10-‘13 LEs and TEs. The SR5 in those years did not come with it from what I can tell.
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I have the scan guage on all the time .. 2016 runner. the voltage on cold start 14 volt range. when its warm/hot out the higher the air temps the lower the volts. 90F ac on the voltage is 13.1-13.4 volts..
air temps 20F 14.5volts.. this is why the voltage changes it is the voltage regulator ..
possible you could have fuse fingers corroded .. high moisture can cause this issue .. others also commented on how their voltage was as the same as my voltage operation..

on a GM vehicle the voltage stays at 13.7 volts when engine is running at normal temps.. when the air temp goes below 20F 14.75 volts sometimes 15 volts on cold start..
 
KP Texan said:
Just replaced the 4 year old battery in my 2012 since it wouldn't hold a charge, and I've been watching the voltmeter much more closely over the past few days. Voltage seems to be normal and stays fairly steady (14.0 volts or so after I start driving, and then settling to around 13.9 volts).
Click to expand...

Hi KP Texan,

All Alternator voltages fluctuate some, due to what the voltage Regulator's job is. It's there to maintain a safe voltage charge flowing to the battery, ...and... the vehicle's electrical system operation! Voltage flux is affected by, ambient Temperature, load demand fluctuation, wire length/diameter, and distance!

You don't (judging by your statement), have anything 'Abnormal' about your alternator's behavior, so you can just Relax and enjoy the security of the new battery, Okay(?)!

rig, cheers! Lol!
 
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Pull the ground straps on the chassis, frame, and engine and shine them up. Better yet run copper grounds to the body ground locations from the battery. I did this to a celica and the power windows sped up significantly.
 
KP Texan said:
Well, that's a bit unnerving to hear (just remember it's a gif so its playing over and over - the dip only happens once while braking). I'll check out the bulbs and any grounds also just to make sure those are good to go. I hate things like this that may or may not be a problem - I'd almost rather deal with something going out completely than wondering!

[MENTION=83083]rigtec[/MENTION] mentioned "voltage droop" in one of his posts comparing his new high current alternator compared to the stock one. Maybe this is one of the symptoms he's referring to?
Click to expand...

I checked my voltage meter over the weekend and it actually does exactly the same dip as yours, I just never really noticed it! So, no worries, all is normal!!!
 
I replaced my dead battery yesterday and I too was paying some closer attention to the voltage meter in the dash. sits just left of 14v when vehicle is running. sometimes when I press the brakes, same thing happens, slight dip then comes back up. seems to be when I'm stopped in park it's most noticeable, doesn't happen too much when I'm driving. no headlight dimming or interior dimming. all lighting is OEM. edit: I first noticed this when it was cold out and blower fan on full, defrosting windows and high heat setting

I also noticed this happens when I put the truck in reverse from park but don't let foot off the brake. It seems to stay a bit lower until I go back to park/drive/neutral. perhaps rearview camera/reverse lights drawing power or how they are wired. I've seen some posts on other forums with 80 series LC doing the same thing but haven't heard about a 4runner doing it

I assume this is also normal, battery terminals/connections are clean and tight. as rigtec mentioned, the alternator seems to be doing it's job by regulating the charge. you don't know what you don't know, I'm surprised I hadn't noticed this earlier
 
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