Chevrolet Malibu Forums banner
21 - 32 of 32 Posts

·
Registered
Joined
·
58 Posts
Once your batteries get fully charged you'll see the voltage dropping some. I just did a 4 hr ride last weekend in my car and after a couple hours of daytime driving voltage was down to 12.6-12.7. at a steady cruise. Your post got me curious to see what my car was doing so I would occasionally put the voltmeter up on the display.
Funny you mention this...just this morning my voltage dropped down to 13.4 and held there until I got to work (15 min at 14.1, 15 minutes at 13.4). I did one stop/start cycle, right before my ramp, to see if that did anything and sure enough it popped back up to 14.3.

I am one who rarely allows my car to stop/start. I just feather the brake pedal just enough to not engage the system, I hate stop/start.
 

·
Registered
Joined
·
58 Posts
Maybe I spoke too soon...on my way home from work the voltage dropped to 12.8 after five minutes of driving and stayed there the entire way home! I called the shop and they said to bring it in, I dropped it off this evening. Luckily they have free loaner cars.

I don't know whats going on since it worked fine (as far as I know) the night I picked it up. We drove around for an hour and it stayed at 14.0-14.2 the entire time. The following day it worked fine but dropped down to 13.4 on my way home. And then today, it dropped to 12.8. I'm sensing a pattern here...

I figured out they put in an Ultima R111542A unit, not that it should matter but its a data point. Does anyone know the "normal" operating voltage for this engine!? I've always been told the alternator should be putting out 13.9-14.6 while running. What are we missing here?
 

·
Super Moderator
2016 Malibu 1LT 1.5T/6-speed 6T40
Joined
·
3,453 Posts
I think all of your voltage readings have seemed normal. I was actually surprised a tech said the reading should never drop below 13.9. That is bold... and would be suggesting just about every car is defective and needs a new alternator.

Has your car failed to start once replacing the batteries? Has it stalled on the freeway? I'm not seeing actual symptoms other than the concern over the voltage readings.
 
  • Like
Reactions: SilverSport

·
Registered
Joined
·
58 Posts
I think all of your voltage readings have seemed normal. I was actually surprised a tech said the reading should never drop below 13.9. That is bold... and would be suggesting just about every car is defective and needs a new alternator.

Has your car failed to start once replacing the batteries? Has it stalled on the freeway? I'm not seeing actual symptoms other than the concern over the voltage readings.
The car has always started after the new batteries were installed. The car has never stalled on freeway or anywhere for that matter.

I'm starting to think they may not know the intricacies of the 2.5 charging system? I am not versed in the system so I can only go off of what I've read on here and what the shop is telling me. This begs the question...was my old alternator even bad to begin with...

Hopefully they have good news for me today, I will keep this post updated.
 

·
Premium Member
Joined
·
2,526 Posts
Normal
Charging voltage will drop as batteries get fully charged. 12.8v is fine as your batteries are fully charged and system is maintaining the demand. Most of these "techs" don't have a real clue on how things work. High 13's is what they expect to see after a engine start which is the indication the charging system is working after servicing the charging system. Remember a fully charged battery's resting voltage is 12.6v so 12.8v is the system maintaining the battery and meeting the cars demand. Perfectly normal readings. Switching on blowers, rear defrost or even brake lights will raise volt meter voltage readings as system reacts to the loads placed on it.
 

·
Registered
Joined
·
58 Posts
Well I got the car back on Friday evening from the shop. They went as far as contacting a GM tech hotline for assistance troubleshooting. They got ahold of a GM engineer who works with the charging system on this engine and they were able to run data with him. He had them reinstall the old alternator and get baseline readings and also to ensure the alternator was actually bad. They determined it was infact bad based on his input. They said it dropped a diode? Then he had them reinstall the Ultima alternator and get its readings. Based on the data they provided to the engineer, he determined it was working within spec for the system.

Im pretty impressed the shop took it as far as they did contacting GM. I dont know how long they worked on it but it was all covered on the shop warranty.
 

·
Administrator
2011 Malibu LTZ 3.6L V6 Red Jewel Tintcoat
Joined
·
19,762 Posts
When they said it "dropped" a diode, that suggests to me that one of the rectifying diodes failed and was either completely open (no current passing) or shorted (all current passing).

An alternator actually creates AC power and needs to be converted into DC. It does this by means of diodes, which are like one-way valves for electricity.

Imagine that you have 2 cylinders pumping water. If there are no valves to control the water going into and out of the cylinders, then it'll just wander in and out with no real pumping taking place.

Then you put a one-way valve on the intake port and another on the exhaust port of each cylinder. When a piston goes down to draw in water, the exhaust valve closes and the intake opens. When it comes up to pump the water, the intake closes and the exhaust opens. If you have one piston at the bottom of its stroke while the other is at the top, then as the pistons move, one will pump water into the common pipe and then the other does so.

Diodes work much the same way. As the alternator spins, coils of wire and magnets act like the pistons and cylinders, effectively pumping electrons. The diodes keep them all flowing in one direction so they can provide power to the car and recharge the battery.

When a diode fails, it would be just as bad as if that water pump above lost a valve.
 

·
Registered
Joined
·
58 Posts
Thanks for the explanation!

I really hope it was only the alternator and the new one is working properly. One more observation...On my 30 minute drive to work this morning my voltage went right to 12.3-12.4 after I started the car and stayed there the entire way. This was with no AC.

Sidenote: after checking out the engine bay this weekend I noticed something at the bottom of engine bay, below the serpentine belt on a splash guard/tray. Pulled out my "grabber" tool and fished it out. I figured out that it was the back grommet connected to a piece of the lower airbox housing! The tech had broken off the piece when removing and reinstalling the airbox (at least twice). The air filter is now exposed to the engine bay; hopefully the upper seal on the air filter/upper housing is still intact. I will be contacting the shop today.
 

·
Administrator
2011 Malibu LTZ 3.6L V6 Red Jewel Tintcoat
Joined
·
19,762 Posts
Take pictures in case it has to go higher up the food chain.
 

·
Registered
Joined
·
58 Posts
They are replacing the air cleaner assembly today, didn't give me any grief at all.

I also learned from the shop that this system has five scenarios when it will kick into charging mode. I cant remember all of the scenarios, but the main one I remembered him saying was AC turned on with the highest fan setting. This did in fact put my car into charge mode and brought it up to 13.9 and it held there until I turned the fan down. Once I turned it down it dropped back down to 12.6. The manager also learned that our car should not go below 12.5 when operating, this was info from the GM engineer.

I think I'm going to stop monitoring the voltage and just drive the car...its making me crazy. Haha
 

·
Registered
Joined
·
58 Posts
So after driving it regularly for almost two weeks now I've come to the conclusion that its working. I can put the system into charge mode by turning on the wipers. It will go up to 13.9 and hold there until I turn off the wipers. The only weird thing I notice is that my car likes to sit at 12.4 when driving normally with no call for extra voltage apparently. Again, it starts everytime, throws no codes, throws no service charging system messages, and drives fine. Still happy I have a three year warranty with the shop.
 
21 - 32 of 32 Posts
Top