Alternator not charging, but no light

95 Aurora, 180k - So I was driving to work today and the car started acting realy weird...trans shifting out of gear, then all the displays went dead, trouble lights on etc. I turned it off and tried to restart it but it wouldn't crank. I checked the battery voltage and it was around 10 volts. Hmm, looks like a bad alternator I thought to myself. Had i missed the dummy light going off and the DIC Check Charging System message in my haste to get to work?

I let the car sit for awhile, and when i came back the battery had gotten itself back up to 12.2 volts (These AC Delco 6Yr batteries are amazing). It fired up, and I was able to drive it, but this time I was watching the battery voltage. It slowly started working its way down, and when it got under 11 volts it started to exhibit the same crazy symptoms. It ran long enough for me to get the car to my work parking garage. Later, I used jumper cables to charge the battery for a while. I was then able to drive the car home. DIC battery output was never above 12 volts.

On my home though no warning lights ever went on to indicate that the battery voltage was low. But I did set a DTC 16, which is battery voltage out of range. So the PCM knew what was up, but for some reason the dummy light was not illuminating.

Is this most likly an alternator issue, or something else? The alternator is a NAPA rebuild which I installed ~3 years ago. Although it has about 3 weeks left on its warranty, I don't look forward to swapping this out...I never seem to learn my lesson with rebuilt alternators.

Any ideas?

The easiest way to check if the alternator is charging is to start the vehicle and then remove one of the battery terminal wires. If the car dies then its 100% alternator problem.....

I don't think that it is safe to disconnect the battery from the car. The battery stabilizes the entire car electrical system. I think disconnecting it could lead to undesirable voltage and current fluctuations that can damage sensitive electronics. Back when cars were a lot simpler, from an electronics standpoint, this probably wasn't a big deal.

I did some research, and it seems that the built in alternator fault detection mechanism does not always go off when an alternator is failing, so I'm pretty certain now that it is the alternator.

thanks for the input though

remember there is another nut attached to the bolt on the of the alternator that you cant see. so dont get frustrated just feel down there and you will find it.