2009 LaCrosse Battery Voltage Reading Dropping

NittanyDoug

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The battery on my 09 LaCrosse CXL gave up the ghost Wednesday. I did a jump and got it to the parts store and replaced the battery with a new AGM style. On the way to the parts store my battery in the DIC was reading 14.4V. Which I thought was right. Then today just for satisfaction, I look again and see that it starts out at 14.1 V then slowly drops down to about 12.7V. I'm freaking out that my alternator is bad or starting to go bad. But I've searched some and I see something about a "smart" system that may be applying here. Does the 09 have it where it knows the battery doesn't need a full 14.4V to charge so it's only sending 12.7V? I don't want to drop $300 for a new alternator overnighted if I don't have to.
 

SD73

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I don't know anything about the smart system. But that does sound like an alternator problem to me. If it were mine, I'd pull out the alternator and take it to the parts store for a test. They'll do that for free before you make your purchase.
 

NittanyDoug

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I don't know anything about the "smart" charging thing either. I ran out for lunch.... started out at 14 then down to 13 and as I returned it was running 14 the entire way. I never paid enough attention to the readout in the past to see if it did that then or not. Unfortunately none of my local supply houses have it in stock. So I'm either looking at rockauto or amazon to get it faster.
 

bobby49

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In the old days, a decent battery sitting still in a car would have an open circuit voltage of +12.6V, and when it was being actively charged by the alternator, it would generally be around +13.6V.

Well, the new cars are a little different. In the Lacrosse, it can "goose up" the charged output to be as much as about +14.5V. When I first saw this, I was a little alarmed. Then after reading the shop manual on this, I found out that it is fairly normal. The system will crank out that higher voltage when certain load conditions are present in the car. Now, the system should probably not let the open circuit voltage droop down very far. I've been able to start a Buick reliably on about +10V open circuit, but now we are skating out onto the thin ice. There are all sorts of wires and connections between point A (the battery) and point B (the starter or something else critical). Each of those things throw in some measurement uncertainty. As the car gets older and those connections dry out, there is more uncertainty.

When my 2014 model is in a normal cruising state, the battery voltage stays between +13.6V and +14.0V. How it gets this higher (than +13.6V) is a more advanced discussion.
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NittanyDoug

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In some ways I think there could be a "smart" system in mine... My rationale for that is that after the jump start on the totally dead battery, the alternator was putting out all it could to try to charge up the dead battery. Now with the new battery, having been run for a couple hours, has a full complete charge. Turning off/on the few things like radio didn't have any impact as it was a full battery. It probably always at start up attempts to charge at the 14V after start-up and then steps it down once it sees the battery is full.

That's if it has a smart charger in the alternator.

I'm going to grab a jump start pack and toss it in, just in case.
 

bobby49

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Smart charger in the alternator probably is not the best terminology. I would call it a smart voltage regulator. GM probably calls it intelligent power management.
 

NittanyDoug

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I did some digging and it does seem that GM started using the smart voltage regulators around 2004. Not that is is a guarantee mine is or all were. I'm guessing it is based on the one article/pdf I found that was put out by NAPA. It did a nice job of explaining how for the first 30 seconds it goes at full charge and then will wind down (or back up) depending on draw/requirements and that they can go down to under 13 amps.

http://www.esghotwire.com/0213_pit.pdf
 
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bobby49

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That seems like a good article. Thanks.
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tmanp

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I wouldn't worry, mine does almost the same thing and has for as long as I've had the car. When driving the display often either reads 12.9 or 14.1.
 

oldschool

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My 2007 will charge the battery up to approx. 14.5v then takes a break. The voltage slowly drops then the alternator kicks in and starts charging again. I guess it's to reduce drag on the engine and improve gas mileage.
 

douger

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More control of the alternator is done through the BCM and ECM than the voltage regulator by itself. Yeah, you can call it "smart charging" and no, I wouldn't sweat what the voltage reading is. What's important is the current output.
 

jagmanvdp

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I am currently dealing with the low voltage issue also. My car got to the point where it had hard starts and issues with misfiring. I took it in and they said that the ignition module was dying(dead) on two cylinders. It acted up with voltage issues for awhile before the actual code came up and the ignition module was acting up. I had the ignition module replaced and the car runs nice, but still dips into the 12.6 volt range at times....after starting at 14.0 volts. I am investigating further, but am not yet convinced that this is ok for the car.
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bobby49

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One problem with the electrical troubleshooting done by lots of owners has to do with voltage versus current. People will stick an ordinary voltmeter on some test points to look for battery. Sometimes they get weird readings of voltage, and they don't know what it means. Part of it has to do with grounding. For all of these standard cars, the frame has a negative ground. However, there are so many pieces of metal frame and also non-metal parts that finding a good ground can be difficult. This gets especially true if any of the major ground connections have become loose or corroded. When you are tracing out some circuit through the car, you sometimes do it with your voltmeter. However, when you try to follow the ground, you will have a hell of a time following it since ground is normally Zero volts, and that can be hard to distinguish from being an open circuit. You might need to switch over and measure current. For all of those amperes flowing out of the battery on one side, you better have an equal number of amperes flowing into the battery on the other side.

Now, on some Buicks like my 2014 Lacrosse, there is a Hall effect current sensor mounted around the negative wire off the main battery. So, Buick already has one right idea about how to measure and where to measure.

If your electrical or electronic problems get too weird, then try looking for current instead of voltage.
 
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