help - voltage oscillates
 

I flashed back from V4 back to V3 yesterday and noticed today that my voltage is oscillating form 12v to 14v - up and down and wont hold steady at 14V. is this normal? Even if I rev it it doesn't jump to 14v, it just continues to oscillate back and forth.

thoughts?

Are you saying that it continuously oscillates? If so, that doesn’t sound normal. The voltage does fluctuate between 12-14 volts at different times though... but not a constant fluctuation.

If I start the car and let it idle it stays around 14v, however, if I rev the car the voltage will drop to 12V and hold for a while. The AC is on as well btw and its 100 degrees outside.

Do you have a MIL?

there is no warning light that comes on.

I just took it on another drive. I noticed that if I rev the car the volts drop to 12V. If I come to a stop the volts go back up to 14V. I checked the voltage at the battery with a multimeter and it follows what's on the dash gage.

Sounds like it's fine but the service manuals are in my sig line if you want to verify.

I would have thought that revving the engine would have caused the voltage to peak not drop.

Guess not.

I tried looking at the service manual however it’s not very clear what is normal and not normal. It talks about what the battery voltage should be but not necessarily what the correct charging amps and voltage should be at any specific rpm Or how to test it without having hook up a computer to it For diagnosis.

My BRZ does that too, im not too sure why. i cant even tell you when it happens, there is no set of particular conditions that occur when my voltage oscillates. but is not a constantly going from 12 to 14v and back to 12V. sometimes its just hanging out at 12V then jumps to 14V for a little while. there is no noticeable difference in ride.

I just accept it as is, at this point. im also completely stock for now!

And how long has it been this way

Mine is a new 2017, been that way since new. It appears to be programmed into the charge logic. Keep from overcharging the battery, reduce load on engine, or something?

I have a 2017 too, but mine just started doing this after a year of ownership

Also I noticed mine drops all the way down to 12.0V unless I’m decelerating. Only under deceleration does it go up to 14V

Perfectly normal for the 2017+.

Turn on the headlights, it will stay at a steady high voltage.

Really? Wow, I would have thought anything below 12.6v wouldn’t even keep the battery charged.

I have been watching the voltage meter recently. Most of time it is fairly stable at close to 14v, brand new car.

I plugged in a Kiwi3 OBD module for reading values on a smart phone. The voltage readout on the car instrument panel went spastic, dancing all over the place. Unplug the Kiwi - issues gone. I had one cycle right after unplugging it that it was still all over the place. The next cycle it quieted down to a more normal reading.

I cannot tell you what is more accurate, Kiwi or car. The car display may have software in it that takes an average value, while the Kiwi is getting the raw information.

This is all what I refer to as "Spurious Electrons", "Random Lines of Code"

YMMV

It's really fine. The manual doesn't go into detail because the voltage varies so much during normal operation. Like all modern Toyotas, Techstream is a key tool for the 86. I'm annoyed whenever I have to sit in the car with my laptop but I've come to accept the reality that there's no way around it.

BMW's efficient dynamics includes only charging the battery with the alternator when coasting, this is an article that explains it in much better detail (https://www.roadandtrack.com/car-cul...ns-bmw-n63-v8/) but it could be possible on newer cars Toyota/Subaru included this kind of charging system to help with fuel economy.

So on further investigation I noticed a few things:

1 on decel was the car does indeed charge to 14v
2 the doesn’t start oscillating until it’s fully warmed up
3 while cruising the car reads just at 12.0V

Question:

1 does the battery charge with only 12V?
2 if the gauge is showing 12V does that mean the rest of the cars systems are gettting enough Volts to keep things running? For instance the A/C, I the computer etc and still have enough to charge the battery? Or will it drain the battery if I should go on a long trip and don’t have the opportunity to coast.

I have a 2018 and it does the same thing so don't fear that you're in the minority I would say, IF we have a similar system to the BMW (highly likely since efficient dynamics started around like 2008-09 so it would make sense other automakers would include similar systems and processes especially by now) it uses the engine to run all your electronics while moving like it normally would, it just doesnt charge the battery after it has replenished what was lost on start up unless you are coasting, because every little bit helps fuel economy. It would make sense at 14v it is using the extra 2 to charge the battery, and only use the neccessary 12 to run the car systems in short you absolutely have enough voltage to run all of the car's systems. The BMW's eat batteries because to cool down the turbo system it runs the fans long after the car is turned off, and since U.S drivers aren't coasters, over time (about 10,000 miles) the battery runs out. There also may be a completely unrelated reason why our cars do this (14v on coast, 12v on throttle) but if I were you I wouldn't sweat it, it seems pretty normal.

constant 14v
 

I sourced my voltage gauge at the glovebox power plug. With key on and engine off I get a hair over 12v usually. With engine running it stays at 14v.:iono:

I found this info in an information guide regarding changes to the 2017 BRZ:
Battery condition sensor:
The previous (2016 and older) current sensor always maintained control to keep the battery fully charged. The (2017) battery condition sensor calculates the charge status, level of deterioration and internal resistance of the battery from data such as its voltage, current and temperature, and controls charging so that there is always spare capacity available. This allows the recharging rate to be increased when decelerating, which improves fuel efficiency.

I think it’s normal. I’ve noticed my ‘18 BRZ (completely stock, 1600 miles) fluctuate between 12 and 14- not sure if I’ve noticed a pattern to it while driving though.

It was really obvious when I was sitting parked with the ac on on a hot day- when the radiator fans would turn on, the voltage would rise to 14v (the charging system compensating for the extra load). Fans turn off, back down to 12v. This slow oscillation continued while I remained parked.

Yeah. I’ve pretty much determined it’s normal. Just something new I haven’t seen.

It is indeed something new to the 17s. Was one of the many changes.
What is happening is explained well in the update document.

Subaru stupidly programmed the car to let the battery discharge during acceleration a
 

Starting in 2017 forward, Subaru stupidly programmed the car to let the battery discharge during acceleration and stops, doing most of the charging while decelerating only. I discovered this when I parked to listen to the radio for an hour and the car would barely crank. They said it's for "economy" B.S.! This will ruin batteries faster. You can force the car to "normal charge" at 14.2V by turning on the running lights (I drive with them all the time now). Also, if you turn the fan on it will hold at 13.3V. But drive normally and watch the voltage drop from an initial 14.4 at start to around 12.1 in just a few minutes. More on this later as I'm working up a big expose.

I'm an Engineer, I like to measure things.

Champion cut a paste thread resurrection award goes to...
https://cdn.shopify.com/s/files/1/03...G?v=1535488904

Having this same issue with 2017 GT86. But notice that it is also dropping when braking. I would have thought that would be a charge zone! The car is also having trouble starting. I had to charge the battery last night.

I've checked the battery and it's at about 12.4 - 12.8. I've checked for drain when everything is off. And it drops to .01 A. So it doesn't seem like it is losing power at night.

The car/battery is only 2 years old. So I would not suspect it is going and that is causing the extra problems. But, I have seen posts about older FRS/BRZs where the factory battery doesn't last long. It takes a charge and gets to full charge pretty quickly. Then it seems to hold it - until it doesn't.

I'll keep trying to see if I can determine any patterns.

But, I thought I'd see if 12V while braking is not a design feature. Anyone?

Glad to hear the voltage swing is normal (sorta ) My 2020 just did the same thing. Although, the temp outside was in the low 90's. I let off the gas and it returns to 14v. I was concerned that I might be only running on the battery. ( and drain it on the way home and leave me stranded )

Bumping for a new friend