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
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
