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I have 2013 Malibu eco. My problem is my new generator is only charging the battery at 12.5 volts to 12.8. When first start the car it is at 14+ volts slowly goes down to 12.5 to 12.8. The AGM battery is only two weeks old.
68890
 

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Hi, when you say "generator" do you mean the alternator(generator in this case) or do you mean your Generator Control Module? I also had similar problems with my 2013 Malibu LTZ ECO. Ultimately turned out to be my Generator Control Module (GCM). I got one from a junk yard and it resolved the issue. I think you can get them new for less than 400, but with covid, I wasn't able to get a parts supplier to actually ship one - hence the junk yard.

So for comparison, my issues at first were intermittent. Instead of the 14.5 norm, it would jump down to 12+- on occasion. The rear aux. batter would continue to charge as normal. When this problem finally got more than intermittent, the batter was basically at 12+- consistently, then eventually would steadly be at 11.2. Sometimes, the car would go into "battery saver" mode, which causes all hell to break loose, essentially limp mode, no power steering, no power breaks, many lights lit on the dash, etc. and very often the car would need a jump to start after that due to battery being dead. There are a few smaller things you can check first, but ultimately I brought the car to a dealer to diagnose the GCM and they confirmed it was bad. Quoted me $2,900 to repair - I said no thanks. BTW, there is a recall on the GCM so if your's has never been serviced, GM owes you one. But good luck with that. My experience GM plays a little shell game with you, pretending to help, bouncing you back between them and the dealer. You have a better chance of finding the pot of gold at the end of the rainbow.

But before I dove into the GCM replacement, there are a couple of smaller items you can check first. I don't have one of these on my vehicle, but I have seen something called a Stop/Start Sensor which is a small squar thing attached to the end of the negative batter. If I had one, I would have replaced it. Second, keep in mind that part of the job of the GCM is to divert power from the generator to either the front main batter or the aux batteries in the trunk. To do that efficiently, there is a black ring you will see on your negative batter cable through which your battery passes. That is a Battery Flow Sensor. It is supposed to monitor the draw/charge on the batter and when the draw is high on the battery, instruct the GCM to send some juice to the batter. If that is malfunctioning, the GCM never gets the news to send juice to the front main batter. It's a cheap part and can be replaced easily. Also, all your batter cables clean and free of corrosion? Are the battery cables ground clean and free of rust or corrosion? You will see where they attach to the front left wheel well. Clearly visible with the hood open. I have also read that one of the battery cables which attaches to the transmission is known for corroding. Never checked mine, but might be worth a look.

I also had another issue which messed with the charging system. I had a Variable Valve Solenoid go bad on the intake side. It is responsible for adjusting valve height under certain driving conditions. Weird thing about these solenoids, they don't really kick in until you get the rpm's up. So my symptoms were, if I was just putzing around town going to the post office or grocery store, I would not have any problem because RPMs never got to a level to invoke or trigger these solenoids. But once I got up to speed, every stop after that, upon hitting gas, the car would severely stumble and occasionally stall. If stall, the ECO would immediately restart the vehicle. Other weird thing about these solenoid, once I had the stumble, voltage at batter would drop immediately to 12+- and if I let it go, would go into th 11's. If I pulled over, shut the car off and restarted, voltage would return to 14.5, until the next stumble. Anyway, put an ohm meter on the one that was throwing code, the intake side, and sure enough, it was dead. Easy repair, replaced them both and issue is gone. Another thing to note, under many conditions that will cause low voltage with these vehicles, very often the rear battery cooling fan will be disabled by the system and you will sometimes see a code for "battery cooling system". This appears to be temporary situation. I recently ordered a ODB scanner which should allow me to test the fan to insure it is still functional.

Anyway, I'm gonna guess it's your GCM, but you won't know until you get it to a dealer to diagnose.

Also, have you had the codes read from this vehicle?

kd
 

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I called gm dealer and that 1800 told me my car wasn't part of the recall only code I get is P0a90 00. Weird thing is when turn the a/c in the car the power from that generator or alternator will kick up and be 13.5 to 14 volts. I almost want just buy that control module and see
68891
 

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Yeah, that's their standard answer, however, that recall went through several iterations. The earlier recalls advised "test and replace if necessary", the NTHSB then challenged GM's test procedure due to two fires on vehicles that passed their test. Ultimately, it was changed to "replace" on all vehicles. The recall is based upon date of manufacture and not on VIN which is what I'm sure you were told. Anyway, you will be stonwalled if your unit was not replaced. Your only option will be to file a complaint at NTHSB and if you're really pissed, sue them. In any event, the part cost me $120 at the salvage yard and about the same to have it installed by a local mechanic. It didn't need to be reprogrammed but I will eventually have it reprogrammed just in case. I think that model scanner in your pic can reprogram those units in any event. So yeah, if you want to cut to the chase, maybe just swap it out and see. Would have saved me a lot of time if I had done that. Also note, you may have a tough time having your non-dealer mechanic work on this part due to all the high voltage involved - all the orange stickers scares some of them.

BTW, that code says historical - is that still an active code on your vehicle?

Hopefully someone on here can help you diagnose it better than I can - I'm not a mechanic except when I'm in my driveway.
 

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Update I changed that battery volt sensor it work for a week at 14+. Then it started doing same thing, I did order a new generator control module from the dealer I will install it this weekend and see what happens
 

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Yeah, these cars seem to have a mind of their own. There's some nasty voltage back there, might want to be sure you follow all safety procedures for working on the GCM. So yes, after changing my GCM and my VV solenoids, my voltage has been right as rain at 14.5. But yesterday out of the blue, it's now decided to run the battery at 12.5 ??? not sure why. No codes. I did notice on the meter there is an item called 14 volt set point - not sure what that is, but I will have to investigate further. Good luck with your part swap. Just in case you're not aware, that GCM will have to be programmed.
 
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