Alternator not charging but no messages or battery light on.

[Cutlas400]

I have a 2007 Buick Lucerne with an odd issue. Changed alternator last year because it failed. The service charging system message along with the battery light would come on and off when driving. Alternator was in rough shape when removed. I replaced it with a new GM alternator and light went out. No messages when driving. New battery also. Parked it for ala year because of medical issues. A few weeks ago I went to drive it and the battery was low, cranked slow but started. I pulled the battery out and charged it, seemed fine. Drove it for 2 days and battery went dead. No battery light or messages at all. I charged battery again, instead it. Same is. Checked it with my Guage and it reads 11.7 when running. No battery light or messages at all. Any ideas? Still recovering from back surgery so I am in no shape to pull the bumper or get underneath it.

 

[2007LucerneCXL]

The voltage is too low, have the charging system checked.

 

[Cutlas400]

The voltage is too low, have the charging system checked.

I don't think you read my post. I understand it's not charging. I'm trying to troubleshoot both issues. The fact it isn't charging and why the system isn't recognizing the charging issue.

 

[2007LucerneCXL]

I did read your post, if the alternator is not putting out the correct voltage it is the likely suspect. The warning message I believe will come on once it goes below 11 volts. The one other item is the voltage sensor #26 which could have failed, note that there are 2 different sensors one for a 5V and one for a 10V for the BCM

 

[HotZ28]

Ia addition, if you have a dead cell in the battery it will not charge. You let the new battery set for a year without charging and that may be the issue. Get the battery load tested!

 

[Cutlas400]

Ia addition, if you have a dead cell in the battery it will not charge. You let the new battery set for a year without charging and that may be the issue. Get the battery load tested!

Battery tested fine, it's actually in my suburban now. And another battery is in the Buick doing the same thing. So I can rule out the battery. Thanks though.

 

[Cutlas400]

I did read your post, if the alternator is not putting out the correct voltage it is the likely suspect. The warning message I believe will come on once it goes below 11 volts. The one other item is the voltage sensor #26 which could have failed, note that there are 2 different sensors one for a 5V and one for a 10V for the BCM
View attachment 48821

Does either of the voltage sensors affect the battery light on the dash? And does either sensor affect the ecm 5v signal to the alternator?

 

[2007LucerneCXL]

If the voltage doesn't drop below a certain level at the sensor it wouldn't set off the battery light.

 

[2007LucerneCXL]

The sensor I assume will set a battery light if the voltage drops below a certain threshold, 11V but would need to confirm, to the BCM. But checking the alternator output is the fastest way, I am unaware of a test on the sensor other than possibly using a Tech2 or similar scanner.

 

[HotZ28]

Can you get the alternator tested! Did you get any warranty with the new replacement that you had installed the past year?

 

[chrisbek100]

I have a 2007 Buick Lucerne with an odd issue. Changed alternator last year because it failed. The service charging system message along with the battery light would come on and off when driving. Alternator was in rough shape when removed. I replaced it with a new GM alternator and light went out. No messages when driving. New battery also. Parked it for ala year because of medical issues. A few weeks ago I went to drive it and the battery was low, cranked slow but started. I pulled the battery out and charged it, seemed fine. Drove it for 2 days and battery went dead. No battery light or messages at all. I charged battery again, instead it. Same is. Checked it with my Guage and it reads 11.7 when running. No battery light or messages at all. Any ideas? Still recovering from back surgery so I am in no shape to pull the bumper or get underneath it.

From what you described it seems you have determined the problem is not the battery as you can fully charge it and it works in another car.

You have also tried a working battery from another car and the problem is still occurring.

Sounds like the alternator is not charging the battery while the car is running.

When the car is not running the battery if healthy should be roughly 12 volts to 12.6 volts approximately when fully charged.


If you take a multi-meter to the battery and start the car the voltage should drop to 11.5 volts and then alternator should kick in and cause the voltage to climb up eventually to 14 volts to 14.6 volts (depending what you have running for accessories) and remain there while the car is running.

From what you describe it sounds like the alternator is not working and charging the battery as you said yourself that the car is running at 11.7 volts.

Do a visual inspection of the alternator. See if it is connected correctly. There is also a plug that goes into the alternator. See if the plug connector is seated in right.

See if you can get the alternator tested somewhere.

That is my best guess.

2007LucerneCXL seems to also have pointed you in the right direction as well.