First off, I'll say I have always had a couple of amplifiers in my car for my stereo. I recently changed out one (for the subwoofer) and installed a slightly larger one....nothing major...just slightly higher wattage (went from 600 to 800 watts). While testing everything, I plugged in a voltage monitor to my dash power outlet (cig lighter for you seasoned folks). It was showing around 14.4 - 14.6 volts with the engine running. Yesterday afternoon, I glanced down and noticed that the voltage was dropping slowly. It dropped down to 12.8 volts and stayed. Even when I turned the stereo, the A/C and everything off, the voltage stayed at 12.8 volts. I went to the parking lot at my work, parked and shut the car off. The voltage read 12.3 volts. Just curious, I tried cranking it to see if I needed to arrange a ride home. It started fine and the voltage jumped back up to the 14.4 range. Again while driving, the voltage would drop to 12.8 volts....but would creep back up from time to time.
So far, I have not had any issues starting the car and no dim lights (I drive to work in the dark). I was under the impression that the alternator put out 14+ volts all the time.

Any ideas? I assume that if the local parts store tests the alternator, they will also see anywhere from 12.8 - 14.6 volts, just like I do. Would that indicate a "bad" alternator, or failing?

**This is the original alternator that came with my 2009 HHR LT 2.2L.
**Battery is a few years old, but not the original.

Thanks in advance..

 

Take it to the local parts store and get a free battery load test, as well as a charging system test.

 

We have a digital regulator, it supplies what is needed. Up and down is voltage is normal.
Not old fashion charge/no charge regulators.

 

Battery load test, double check the wires to that new 800 watt amplifier
test the charging system.
I think loose ground or dying alternator

 

Thanks for the input. I will have the local parts place check it.
When swapping the amp, I only made changes at the amp end of the setup....nothing changed on the battery end.
If anything, I would suspect a dying alternator....but will have it checked to hopefully confirm one way or the other.

 

Don’t forget our discount at RockAuto!

 

What DonBrew said. This sounds normal to me. Regulated Voltage System. My 2008 Sierra has it, and the truck has a real time volt meter. When I first got the truck I thought something was wrong. Perfectly normal though. In fact now I get concerned if the voltage doesn't drop while driving. It does not drop when the outside temperature is below 40 or 45, or above 85 or so. It looks like this has been discussed before.

https://www.chevyhhr.net/forums/prob...m-works-58456/

AGCO Automotive Repair Service - Baton Rouge, LA - Detailed Auto Topics - Why GM Voltmeters Show Low Voltage

 

That's why they don't put it on the dashboard. Too much information is dangerous.

That silly looking plastic thing wrapped around the negative battery cable is the current sensor; it tells the BCM what the demand is.

 

***UPDATE***
Had the battery tested at two different chain stores....both say battery is good.
Removed and tested the alternator since I live way outside town and didn't want to risk driving it there. Store said alternator is also good.
So today on my way to work, the voltage started dropping 1/10th of a volt every 60 seconds (average). It had 12.6 when I left home. By the time I got to town, I was down to around 9.8 volts....then stuff started shutting off.
Power steering, traction control, ABS, etc....then the engine. Had it towed the rest of the way to the dealership for diagnosis since it appears that the system isn't telling the alternator that it needs to make voltage.
I won't have a diagnosis until tomorrow, but they had to connect a jump box in order to roll up the windows (forecast to rain). It started up with no problem and he could tell that the alternator was not charging....but I already figured that part out.
He said that Autozone is known for getting alternator checks wrong and their machine only shows pass/fail (not actual voltage output) and it would have been a very minimal voltage needed to pass. Still could be the alternator....or worse, the BCM.

 

Let's hope for the best then.....