Voltage Wayy Too Low

[carter1551]

I just replaced my alternator and battery and was driving home tonight and the whole way home my voltage was under 12. The battery light never lit up and i even tried to load the electrical system even more and everything functioned fine with no dimming of any sort. I got home and shut off my car and it actually jumped higher once it was shut off. It was still under 12 volts but jumped up a few tenths. All these readings were all through my scangauge. Anyone got any ideas as to what the issue could be? Im thinking that the reading is innacurate because if the voltage was really that low my battery light on the dash should have come on right?

 

[TheMAN]

you need to be testing the voltage right at the battery instead!

 

[carter1551]

let me give you a bit more info. i replaced the battery a month or so ago. Then a week ago my battery light comes up and my voltage is way low according to my scangauge. I have autozone check battery and alternator and he tells me my alt is bad. I take it off the car and to an independent shop to confirm it and they tell me the same. I installed the new alternator a few days ago and havent had any problems aside from the voltage being listed low ACCORDING TO THE SCANGUAGE. I will test it at the battery in the morning like you suggested theman

 

[Alejo_NIN]

some say this is a really bad test that can actually damage your vehicle, i do it all the time and never had an issue. what i do is while the engine is on, i unplugg the battery. usually if the car dies it means the alt is bad. it may also start idling erratically in which case it might be that the alt is not giving enough juice and relies on the batt to compensate, reaosn being why batteries go bad so quickly.

i take no responsability for this test.

 

[BlkWidow]

some say this is a really bad test that can actually damage your vehicle, i do it all the time and never had an issue. what i do is while the engine is on, i unplugg the battery. usually if the car dies it means the alt is bad. it may also start idling erratically in which case it might be that the alt is not giving enough juice and relies on the batt to compensate, reaosn being why batteries go bad so quickly.

i take no responsability for this test.

I have done this to my other cars

 

[03zoomzoom]

That is the old fashoned way to test an alt. I would no do this on a car built after 1995. There are diodes set up that function different elements of the car and will be damaged if the car is running without a battery.

some say this is a really bad test that can actually damage your vehicle, i do it all the time and never had an issue. what i do is while the engine is on, i unplugg the battery. usually if the car dies it means the alt is bad. it may also start idling erratically in which case it might be that the alt is not giving enough juice and relies on the batt to compensate, reaosn being why batteries go bad so quickly.

i take no responsability for this test.

 

[Alejo_NIN]

That is the old fashoned way to test an alt. I would no do this on a car built after 1995. There are diodes set up that function different elements of the car and will be damaged if the car is running without a battery.

what is a DIODE?
where are they located?

please, no wiki-links.

 

[03zoomzoom]

A diode lets electricity flow in one direction. They are located all over the electrical system.

what is a DIODE?
where are they located?

please, no wiki-links.

 

[Alejo_NIN]

A diode lets electricity flow in one direction. They are located all over the electrical system.

just testing....

yeah, that's why i said it was risky to do it

 

[03zoomzoom]

I got ya. ha ha ha. I've been in parts for 6 yrs now. I would have to turn in my ASE cert if I didn't know that question.

just testing....

yeah, that's why i said it was risky to do it

 

[P-Funk!]

Diodes rectify the AC into DC when bridged...

Agree - do not simply disconnect the bat to troubleshoot the system.