# Service Battery Charging System



## ChevyGuy (Dec 13, 2014)

The car uses an advanced charging system. In order to save fuel, it tends to lower the voltage when you accurate, and raise it when you coast. It's not the old "14.4V all the time" type system.

That said, I'm not sure what's going on. Are you able to pull a code? Have you had the battery load checked?


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## WilliamC283 (Sep 21, 2019)

Battery is also less than a month old as well. The only thing I’ve not replaced with a factory replacement is the Negative battery terminal. Had went to advanced and got one that they sale and it was just worse, so I put the old one back on. Also after alternator was changed once the car has run for a few minutes there like a chirping noice that comes from the alternator. Was thinking maybe just got a bad alternator.


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## WilliamC283 (Sep 21, 2019)

Does anyone have any ideas on what could be causing the issue with my Service Battery Charging System light to be coming on and off. It’s the only issue I’m having with this car and I have already replaced the bulk of everything. Does anyone think that I should change the BCM and Negative Battery Terminal. Running out of ideas, I’ve literally done everything I can think to do. Went today and had the Battery load tested even though it’s only a month old.


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## ChevyGuy (Dec 13, 2014)

Too broad. You'll need to check for codes. Many parts stores will do it for free.


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## WilliamC283 (Sep 21, 2019)

Without check engine light or the Service Battery Charging System light there will be no code to read or I would have already done it. The battery light only come on when giving the car the gas, doesn't come on if it sitting at an idle.


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## ChevyGuy (Dec 13, 2014)

The system keeps a history of codes. As long as too many key cycles haven't passed since the last time it came on, a code reader should still be able to retrieve it. 

The only thing I could find in my book is that the light will light if either the charging voltage or battery voltage goes outside of 11V-16V range. It looks like it also lights on certain codes. You might want to rig a voltmeter to see what's happening. Normally, when you give the car gas, the charging voltage will drop so the engine has more power. But either it's not under control (causing it to rise) or the battery isn't able to keep the voltage up (meaning we're back to battery or battery cable.)


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## WilliamC283 (Sep 21, 2019)

Okay, well other than the volt meter in the cluster I have took my volt meter and tested it. Without the car running it shows 12 volt. When started and at idle it is 14.6, when revved up to about 1500 to 2000 rpm and held it drops all the way down to 11.9 and 12 which is exactly what the information center in the car reads when I’m driving it which causes the light to come on. 

The list of things that have been replaced in the last month are: Alternator, Belt, Idler pulley, Battery, Battery Control Sensor. Also had to replace pcv valve yesterday due to vacuum leak. Took the car to the parts store today and had a load test ran on the battery and it completely tested good.

I will take it tomorrow and have the computer scanned to see if I get any codes. I just figured since everything else has been changed the only thing it can be now is the Negative battery terminal or the bcm. I did buy one of the replacement Negative terminals from the parts store but it made it worse, so I put the original back on. Was going to order a factory replacement AcDelco and replace it with.


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## WilliamC283 (Sep 21, 2019)

Also the only other things I have noticed is that when running at night the headlights will dim. I just figured that was due to my Voltage fluctuating. But the will even dim and go back to normal even at idol. It has a chirping noise that come from the alternator are after the car gets up to normal running temp. It never done that until after the alternator was changed which is what lead me to believe that might have just got defective one. Other than that the car runs pretty smooth now that the pcv valve was changed.


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## plano-doug (Jul 1, 2015)

WilliamC283 said:


> I will take it tomorrow and have the computer scanned to see if I get any codes. I just figured since everything else has been changed the only thing it can be now is the Negative battery terminal or the bcm. I did buy one of the replacement Negative terminals from the parts store but it made it worse, so I put the original back on. Was going to order a factory replacement AcDelco and replace it with.


I agree, change the negative cable and see what that does. Usually, from what's been posted here, the bad negative cable would have other symptoms as well. But fingers crossed that fixes it for you.

After that, I'd focus on the replacement alternator. Was it a reman? What you describe sounds like a voltage regulator issue, which is in the alternator. I've seen a few cases where fresh-out-of-the-box remans didn't work very well. (These were not on Cruzes, which are even more sophisticated, but they were remans.)

Doug

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## ChevyGuy (Dec 13, 2014)

plano-doug said:


> What you describe sounds like a voltage regulator issue, which is in the alternator


I'm pretty sure that's done by the BCM. That's how it controls the charging voltage. It sends a PWM signal to the alternator. But that's not to say there isn't some kind of amplifier or controller in the alternator to step up that signal to the field.

I'm wondering if a phase or diode is bad in the alternator. A scope would answer that pretty quick, but most people don't have one.


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## snowwy66 (Nov 5, 2017)

Do scopes still exist?

One would have to take the alternator apart and measure resistance on the diodes. The diodes are one way. 2 diodes per phase. It's what converts the alternating current to direct current. 3 phases X 2 diodes per phase. 6 diodes. 

Where was the alternator bought? From what store. Not all stores sell good quality parts. And as mentioned. Once in a blue moon a new part turns out to be bad.


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## WilliamC283 (Sep 21, 2019)

I’m not sure where the garage got the alternator from. The guy I bought it from had just had it changed. Gave me all the receipts from the wrk where it had just been done. I never trust receipts so i went through and looked at every part that had been replaced. The car sounds good when you first start it up but after it warms up you can here a chirping noise come from the alternator. I was thinking maybe the new alternator had faulty brushes in it. Just my thought. Now i know why he was selling it though, he was tired of chasing a ghost.


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## plano-doug (Jul 1, 2015)

ChevyGuy said:


> I'm pretty sure that's done by the BCM. That's how it controls the charging voltage. It sends a PWM signal to the alternator. But that's not to say there isn't some kind of amplifier or controller in the alternator to step up that signal to the field.
> 
> I'm wondering if a phase or diode is bad in the alternator. A scope would answer that pretty quick, but most people don't have one.


Without a manual specific to the alternator, I can only speculate, and so I shall  

I would expect the BCM to signal the alternator for high-low-nom, but not via PWM, unless that's just describing some sort of very rudimentary communication. On these modern, high-current alternators, I would expect the PWM'ing to be happening between regulator and rotor windings. I can see how having the fast edge rates associated with chopping the drive signal into the rotor will make for generating more power, but I would expect that loop to be closed locally by the regulator, not remotely by the BCM.
...
My first (and only) alternator rebuild was on my 1981 Buick Skylark, FWD x-body. The diode trio had a bad diode. It is used to drive the indicator light on the dash, but provides no essential function for making the alternator work. You could remove the trio with no impact on the voltage regulation of the alternator. This is a classic example of how adding test circuitry can negatively impact the reliability of a system. I still advocate for test features, but thought the irony worth mentioning 

Doug

.


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## WilliamC283 (Sep 21, 2019)

Update on the car: Now it doesn’t Idle smooth but when you give it the gas it smooths out until you let off the gas.


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## ChevyGuy (Dec 13, 2014)

snowwy66 said:


> Do scopes still exist?


Indeed they do. The question is how common are they for automotive use.

Alternators are 3-phase devices (think of it as the electrical equivalent of a 3 piston pump with an even "firing order"). If one, or two phases are out, they'll still generate power, but not as much as normal and the drag on the pulley will not be even. That's why the description of a noise on the belt has me thinking along those lines.


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## ChevyGuy (Dec 13, 2014)

plano-doug said:


> Without a manual specific to the alternator, I can only speculate, and so I shall


I checked my book. I was a bit off.

The BCM takes voltage and current measurements and the ECM controls the alternator. The two talk via the car's bus. According to the book, the ECM sends a "duty cycled voltage" to the voltage regulator (in the alternator). The control module in the alternator uses PWM on the field winding. It also sends a PWM signal (the same one?) to the ECM so it knows what the alternator is doing to anticipate the alternator load. 

There's any number of places this system could detect problems. Getting the codes will help know what the computers are complaining about.


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## RachelM (Aug 24, 2021)

WilliamC283 said:


> Does anyone have any ideas on what could be causing the issue with my Service Battery Charging System light to be coming on and off. It’s the only issue I’m having with this car and I have already replaced the bulk of everything. Does anyone think that I should change the BCM and Negative Battery Terminal. Running out of ideas, I’ve literally done everything I can think to do. Went today and had the Battery load tested even though it’s only a month old.


250amp fuse on the battery!!!


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## Jorgem (Nov 16, 2021)

WilliamC283 said:


> I just bought a 2014 Chevy Cruze with 30,000 miles. I keep having the Service Battery Charging System light come on. When at a idol the battery voltage has 14.6 but as soon as you give it the gas the voltage will start dropping down to 12 volts and below. The alternator, surpentine belt, idler pulley, battery control sensor and pcm have all been replaced within the past month. Has anyone else had this problem and what can I do to fix it. I bought the car with the intensions of giving to my daughter for her 16th birthday.



Have you figured out the problem yet I've just recently started having the same issues I haven't replaced the computer yet my next step is to go through all the wiring and connections and make sure there's no corrosion and that everything is clean


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## RachelM (Aug 24, 2021)

Jorgem said:


> Have you figured out the problem yet I've just recently started having the same issues I haven't replaced the computer yet my next step is to go through all the wiring and connections and make sure there's no corrosion and that everything is clean


 My problem was the large fuse on the battery itself.


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## Jorgem (Nov 16, 2021)

RachelM said:


> My problem was the large fuse on the battery itself.





RachelM said:


> My problem was the large fuse on the battery itself.



I've checked it. Looks good. The car runs fine just shows battery light and service charging system message. Goes away after a bit then doesn't come back for a couple of weeks


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