LS1GTO Forums banner

1 - 8 of 8 Posts

·
Registered
2005 Pontiac GTO
Joined
·
3 Posts
Discussion Starter #1
Hi all, this is my first post and I did a little digging but couldn’t find anything related to this.
Issue: Alternator light comes on during start up and voltage reads low (9V)

Troubleshooting so far: Alternator charges fine (14V with everything off except engine/13.5 once everything is on)

I have been having this issue for awhile and typically once I put it in gear to start driving or rev the engine to 2k RPM the battery voltage would kick in to read around 13.5V. However, it has consistently taken longer to ‘fix itself’. I am assuming with all this data that the issue is due to the voltage sensor, but I am unsure where exactly that would be. I would assume connected to one of the battery wires but I can’t find that. Anyone have a picture of what the voltage sensor would look like or where to find it?
 

·
Worthless reject member
Joined
·
46,561 Posts
our cars do not have a seperate voltage sensor.

iirc, the BCM and the ECM can read system voltage on their own.

your issue is likely due to the battery.
 

·
Administrator
Joined
·
9,524 Posts
Update your profile so we know what car you have, the 04 is different electrically from the 05/06. 04 has an internal regulator in the alternator, 05/06 uses the ECM for field coil control.
As suggested the battery should be tested to make sure it's good and charged or replaced as necessary.
13.5V is somewhat low especially if the engine is cold, initial charging voltage should be 14+ and drop to about 13.8 at operating temp. It's a 140A alternator so the voltage should remain stable with anything but a very heavy load.
 

·
Registered
2005 Pontiac GTO
Joined
·
3 Posts
Discussion Starter #5
Ok, not sure how to update my profile yet, but I have an '05 GTO. Why would it be the battery if I am getting fine read outs when I check the battery voltage using a multimeter? My issue is that the car gauge read out and the multimeter do not match.
 

·
Registered
2005 M6 MBM GTO
Joined
·
66 Posts
Ok, not sure how to update my profile yet, but I have an '05 GTO. Why would it be the battery if I am getting fine read outs when I check the battery voltage using a multimeter? My issue is that the car gauge read out and the multimeter do not match.
I don’t know anything about the voltage but click on your account photo at the top of the page and go to account settings and there’s a place to put your vehicle details in there.
 

·
Registered
2005 Pontiac GTO
Joined
·
3 Posts
Discussion Starter #7
I don’t know anything about the voltage but click on your account photo at the top of the page and go to account settings and there’s a place to put your vehicle details in there.
Just figured it out thanks!

As suggested the battery should be tested to make sure it's good and charged or replaced as necessary.
13.5V is somewhat low especially if the engine is cold, initial charging voltage should be 14+ and drop to about 13.8 at operating temp. It's a 140A alternator so the voltage should remain stable with anything but a very heavy load.
I would also say it's probably closer to 13.8V once turned on. My multimeter is not digital so not super accurate but there were times when it was clearly reading above 14 so I know the alternator is doing it's job. I will say when cranking to start the starter does struggle...another issue that is likely related to the battery. I just want to understand the logic of why the battery would charge and hold a charge but would cause these issues. Trying to learn as much as I can!
 

·
Worthless reject member
Joined
·
46,561 Posts
The way i read your post, your voltage dips to 9 volts while cranking, which is a bit too low.
The starter draws quite a bit of current, but will not see that large of a drop. Usually a battery that has a low charge or has sulfated and lost its capacity can cause a large voltage drop while cranking. Or the starter motor is drawing too many amps, or a wiring or connection issue.

If you meant that right after engine startup you have the low voltage issue, but your battery reads 13.5-14 volts, then your issue lies elsewhere.

There is typically a small drop in voltage displayed on the cluster or reported by the OBD PID for system voltage, and the voltage read at the battery, but it is not much.
 
1 - 8 of 8 Posts
Top