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Ok, I'm a little confused... How much should we be seeing on the voltage drop while driving with lights, radio,etc on? I am seeing anywhere from like 13 - 14.8 while driving. I already had the neg battery cable replaced, the battery was checked out and they said it was fine. When the voltage drops I can tell the difference on how the car responds. Any suggestions? Maybe a bad cable again?
 

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Ok, I'm a little confused... How much should we be seeing on the voltage drop while driving with lights, radio,etc on? I am seeing anywhere from like 13 - 14.8 while driving. I already had the neg battery cable replaced, the battery was checked out and they said it was fine. When the voltage drops I can tell the difference on how the car responds. Any suggestions? Maybe a bad cable again?
Anywhere from 12.x to 15.2 while driving is completely normal, depending on what's switched on and what the current battery level is.
 

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I got 13.8 right now (headlights and fogs on, blower off)...just kidding it went to 14.0.......14.2......14.0......14.3. (Fluctuates a lot). I see 14.7 a lot too. Usually though, it's at 13.8. I used to get 12.8 all the time but I think my battery is getting weak.


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Just indicates it's charging the battery. 12.8V is cruising along with the alternator switched off and just holding battery voltage.
 

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12.8V is cruising along with the alternator switched off and just holding battery voltage.
Anything below that suggests it's discharging the battery - at least on the gasser. I'm not sure what might be going on with the diesel and the AGM. But I don't think the voltages are all that different.
 

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Anything below that suggests it's discharging the battery - at least on the gasser. I'm not sure what might be going on with the diesel and the AGM. But I don't think the voltages are all that different.
Yeah. And they do that sometimes as well, for instance, under acceleration. The voltage management program can be hard to follow, but if you're not having random electrical issues or a battery not holding voltage at shutoff, everything should be working as intended.

If you consistently see high charging voltages pegged in the high 14's-15 (I saw these a lot last winter with a bad battery), you may want to consider having the battery or cable tested.
 

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Depending on charge mode, mine varies from 12.2 to 15.1 volts. This is all normal, according to the manual and what charging mode it is in. I've seen it dip to 12.1 while cruising, but then it jumps back up to 12.2. I've also seen it hit 15.2 (when cold) for a few seconds, and then back down to 15.1. Mine is the diesel with the AGM battery.
 

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According to this chart if you're at 12.6V or below on a AGM, you're at 75% capacity, or 25% discharged.

If you were cruising along at 12.2 and pulled over and stopped, the re-start could be interesting.

There's only two reasons I can think of for it to be that low. The computer might have turned off the alternator for acceleration and forgot to turn it back on, or the battery current sensor is showing a high charge current.

If it was me, I think I'd set up Torque Pro with graphing and monitor some things to see if I could see a pattern.
 

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I can confirm that a Cruze can still start at voltages THIS low...

Course, you could probably start this motor with a pull-string were one attached :D



If it drops to 12.2 while driving, you might indeed have a battery cable issue. My car seems to like to keep my new AGM battery "charged" to 12.5-12.6V.
 

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Discussion Starter · #30 ·
Don't agree with that huge voltage variation. Get yourself a digital voltmeter like this one, 12 bucks on ebay or one equivalent, you want a 200 millivolt range.

Pro Digital Voltmeter Ammeter Ohmmeter Multimeter Volt Tester Meter MS8233B Le | eBay

With the engine at idle, blower at max, head lamps on, 200 mv DC range, touch one probe directly to the negative battery terminal, not the cable clamp. Other to where its grounded next to the radiator. Should read less than 10 millivolts. I was reading 2.1 volts on mine with this problem. Do the same for the positive battery terminal to that aluminum plate.

Typically all these parts are the same, taking my old negative battery apart, namely the clamp end, very poor point contact connection in there. New cable with the same test, instead of dropping 2.1 volts, dropped down to 0.0047 volts or 4.7 mv. My positive clamp was good at 6.4 mv.


All that reving and so forth that jblackburn did, under various loads, held constant at 14.7V on the DIC. When the temperature was like -30*F before this problem occurred, was reading around 15.1V, normal, the colder it gets, the higher the charging voltage needs to be.

At 105*F, will drop and hold at the 13.5 volt range, so-called negative temperature coefficient of a battery.

Reason why mine was dropping well below this range, that extra 2.1 volts added to the voltage regulator setting, kicking the alternator into overvoltage mode where it will completely shut off. And the DIC was not constant, always varying between, 12.6 volts and 15.5V.

On checking the state of charge of the battery, was low at 12.4 volts, even under no load with the bad cable, that after running the engine for awhile, then shutting it off, read 12.9 volts at 70*F, now its fully charge. That low charge leads to sulfation, more problems.
 

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Decided to graph the battery voltage on my phone app with an OBD2 dongle on my 40 minute drive...min value was 13.5V, max 14.4. And yes, I had floored it a few times in this drive. Doesn't seem to change the voltage when I do. For most of this, the blower and headlights were off. I did turn the A/C on full blast for a minute...no change in voltage. It was 14.4 at that time. Very interesting stuff.
 

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min value was 13.5V, max 14.4.
Between 13.0 and 15.5, I wouldn't worry about the voltage. It may vary depending on underhood temperature and charge state of the battery. If possible, graph the battery current as well. That may tell the story.
 

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Discussion Starter · #33 ·
Early automotive systems did use current as an indication of the state of charge of a battery. Used a zero center ammeter when the meter switched to the right with a + sign, battery was charging, meter was located in series with one of the battery leads. Or to the left, -, was discharging. With 6 volt systems, and a brush type generator, discharging was quite common at idle.

The way you knew your battery was fully charge is to drive at above 1,500 rpm, and the needle was at zero. If you had problems starting your vehicle draining the battery, that needle would swing as far to the right as it could because the battery required to be recharged. But once charge, meter would center, switching on the head lamps, didn't make any difference, the output of the generator had to increase, but as long as the battery was fully charged, that needle would stay at zero.

This switch later on, memory is shot, can't recall the year to monitor just the voltage. In a sense, an assumption as long as the voltage was there, the battery was fully charged. But with several complete discharges, the capacity of the battery would greatly decrease, least the current indicated whether the battery could take a charge okay. Technically, you need both current and voltage to know the condition of the battery.

But batteries can be tested for this by external means.

With charging voltages, this varies considerable with temperature and not any temperature, but the actual temperature of the battery. Vehicles of the 60's were very strong on this issue, the voltage regulator with temperature compensation to precisely match that of the battery, was mounted very close to the battery. Not only ambient temperature, but underhood temperature as well.

All this was tossed out the window by mounting the voltage regulator inside of the alternator, with heavy loads, AC, head lamps, electrical defrosters, high powered audio systems, etc. Insides of that alternator would be running red hot, result, undercharging the battery. This is where our Cruze's plus many other vehicles are at today.

Not the right way of doing this, but the cheapest way. Over charging a battery is just as bad as under charging it, overcharging creates bubbles on the plates, and increases evaporation of the electrolyte, could be replaced with a battery with caps on it, but can't we a so-called maintenance free battery, no such thing as maintenance free, even like in a ball joint that needs a shot of new grease every once in a while, they like the battery wear out much quicker. Plates in a battery will buckle with overcharging causing short circuits, but at first, high self discharging rates.

Undercharging causes sulfation of the plates, a hard like substance that the charging current cannot penetrate.

Ha, good engineers like me, know how to do this right, but can't fight the bean counters. Either you do it their way or they will find somebody that will. Not good when you have kids to support. Just saying, don't blame engineers in any phase of automotive design. Back in the 60's, GM was ran by engineers, that sure changed over time. Are CEO's really worth that much? Most I met would be dead without some intelligent support.
 

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Some cars had ammeter, some had voltmeters. Both have their limitations. You really need both to have a full picture.
 
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Discussion Starter · #35 ·
How about a good oscilloscope with both a voltage and current probe, not only shows average, RMS, but peaks as well.

With digital and analog electronics, a good scope is the only means to give one eyes to see exactly what is going on. Automotive is the only field of electronics that does not give precise voltages, currents, and waveforms for testing this stuff.

Instead the idiots that write service manuals only go as far as using an ohmmeter, but when it comes to solid state, they say, DO NOT TEST. That translated into English means you cannot test anything. So they said, just replace with a known good part. How do you know if a part if good if they don't even supply the basic specifications.

In engineering, is nothing except specifications so in effect have the blind leading the blind. When OBD 1 was first introduced, said over 100,000 tech jobs will be created, never happened, so have some guy good at replacing a muffler doing this kind of work at 90 bucks an hour. Doesn't even know the difference between a resistor or a doorknob.
 

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I drove my car for 20mins I actually have a video and every time I coast the car volts shoots up to 14.6 ish and every time I brake or accelerate the volts drop to 12.6. Just driving around with cruse control on stays at 12.6 unless it accelerates by itself at which point it will go up until it is no longer accelerating but maintaining speed.
This is totally normal and operating as designed.

When the battery is fully charged (12.6V), modern GM alternators will decouple under acceleration, and recouple to charge during deceleration. This is done for a small fuel economy boost.
 

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My car does not have a variable alternator. And when I first got the car the range was 13.8 to 14.6 constantly except before start up. I never looked at the start up voltage. The car was running and driving PERFECTLY. Then I took it for a oil change and tire rotation it was fine until I noticed the oil. They pressure washed the engine compartment and now the volts stay 12.6 and the car acts exactly like something is wrong. The volts drop the power steering gets hard randomly the ac blower reduces speed at idle. This is not how my car was when I got it in April and only changed when after being pressure washed.
All Cruzes have one.

The rest of the symptoms make it sound like there's a bad ground connection shared between things, though.
 

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The dealer claimed it was my battery that I had acid leaking out.
This is possible on some Gen I batteries at the positive cable.

https://www.cruzetalk.com/threads/h...s-a-blue-fungus-among-us.226177/#post-3104817

As I had some issues with my phone pairing and that's what onstar had me do to reset the car.
Sometimes a phone does not disconnect from the bluetooth and causes a battery drain.

2) check your neg cable for good ground thru sensor to your body. (see video on youtube if you need help locating)
Consider this also


I also purchased a brand new AC DELCO battery.
Cruze Battery Upgrade Options

1) check if your car is in the NEG battery recall no one seems to know about
Special Coverage #14311: Negative Battery Cable
 
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