what should my voltage be?

I have a 05 aveo. My thermostat housing blew apart and I fixed that all up. At the same time my battery light came on so I replaced the alt. Battery tested good at 709 CCA of 540. Now with new alt the battery light is off but the car runs at 12.5 volts. Is there anything I should check?

And I would like to add I am a ase tech and have checked voltage to alt and and voltage at the voltage regulator. Only thing I have not changed is the battery. This is driving me nuts cuz of the fact I have a 8 month pregnant gf driveing it

12.5V is too low. That is even a little low for the car being off. 12.6-12.8V off is normal. Running, the battery voltage should be 13.5-14.5V.

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Originally Posted by Daox

12.5V is too low. That is even a little low for the car being off. 12.6-12.8V off is normal. Running, the battery voltage should be 13.5-14.5V.

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I get that but I guess I'm really wondering could a bad battery cause that. I suspected a bad alt so I changed it twice. Or is there any problems you guys have came acroo with this issue

Sounds like you're saying the battery light came on immediately after the T-stat blew up, and wasn't happening prior to that. If so, I'm wondering if that flying coolant is somehow causing this. We know that water and electricity aren't friends, and with the stuff going everywhere, maybe some of it is making a partial ground and causing a voltage drop. One thing that comes to mind is the fuse box. I don't know how well that box would shed liquid - perhaps enough of the stuff got into it and leaked down into the area of the big wires. But it could be elsewhere also - maybe pooled around some wire which is out of sight. Lots of speculation here on my part. But being a tech, I think you would have found an obvious problem right away, which is why I'm thinking out of the box on this.

If your battery is bad, it won't get up to 12.5, or it'll get up there super fast. I'd guess the battery is fine, but the voltage regulator on your alternator isn't working properly. I've heard more than one story of people buying alternators that don't work out of the box. To double check, what is your voltage with the car off?

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Originally Posted by avguy

Sounds like you're saying the battery light came on immediately after the T-stat blew up, and wasn't happening prior to that. If so, I'm wondering if that flying coolant is somehow causing this. We know that water and electricity aren't friends, and with the stuff going everywhere, maybe some of it is making a partial ground and causing a voltage drop. One thing that comes to mind is the fuse box. I don't know how well that box would shed liquid - perhaps enough of the stuff got into it and leaked down into the area of the big wires. But it could be elsewhere also - maybe pooled around some wire which is out of sight. Lots of speculation here on my part. But being a tech, I think you would have found an obvious problem right away, which is why I'm thinking out of the box on this.

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Yes I did consider that. But after I changed the alt the battery light is off and voltage running s only 12-13. And everything else I know tells me its wrong should b 14. Unless the alt only charges when its told to

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Originally Posted by Daox

If your battery is bad, it won't get up to 12.5, or it'll get up there super fast. I'd guess the battery is fine, but the voltage regulator on your alternator isn't working properly. I've heard more than one story of people buying alternators that don't work out of the box. To double check, what is your voltage with the car off?

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Voltage off is 12.1, and this is the third alt I've put on in 4 days. Can I really get that many bad ones?

At least 13.5, you could have a bad regulator.

But on 3 diff alts ?

Idk if the regulator is separate or not. Could be ****ty wiring, a short. Do you have a new battery and new alternator both?

Not a batt yet I have a new one in hand for when I get home. I've checked voltage at power supply. Check battery voltage at pink wire on connector from pcm. And power at blue to batt light and all is good. I even grounded blue wire to check light still worked

Well I would try a new battery with the new alternator then check back with us.

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Originally Posted by camopaint0707

Well I would try a new battery with the new alternator then check back with us.

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Battery changed nothing. If the car is only running at 12 v y is my battery light not going on? Its like there is nothing telling the car to charge. Is there a way to by pass the regulator to just see if the alt will charge

I'm not sure what you are trying to say...

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Originally Posted by camopaint0707

I'm not sure what you are trying to say...

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On some gm cars you were able to by pass the regulator by grounding it and the alt would charge at full potential. I'm wondering if there is a way to for so here. And I am also thinking could my ecm b bad does it control the regulator.

I'm just going to return the alt and get a better brand to see if that changes anything if not I'm going to replace the computer. Other than that I'm Sol

Have you taken your car to a shop for this?