last night i was driving my car and noticed the dash lights seemed to be getting dim not much but enough to get my attention so i pull up the battery voltage and its going from 14.1 to 12.9 to 13.4 to 12.2 back and forth this was at a steady speed
it did this till i got home left again about an hour later and voltage stayed at 13.7 -13.8 (normal) the whole time i drove it
so my question is what gives the ac wasnt running
the stereo wasnt loud nothing out of the ordinary
so is it something to worry about seems fine now but concerns me
i think its the original battery in the car from 2001 but that shouldnt affect voltage while running should it

thanks in advance

 

Mine did the same and after awhile the battery just went dead. It was a bad cell in the battery. I replaced the battery and everything works fine now.

 

Let me guess you have an A4....I think the voltage fluctuation is due to the decoupler pulley on the alternator.....My 98 A4 didnt fluctuate until I put on the new style alternator but at least I dont have to deal with the rumble anymore or the belt dust that the old alternator caused!!! Hope that helps

 

You might want to check the voltage regulator in your alternator.
They do wear out eventually.

 

i would hope gm would build an alternator well enough to last more than 30k miles but i dont know

 

I had a slightly corroded positive battery cable lug to positive battery terminal connection cause the exact same symptoms on my '99 'Hoe.

 

I'm sure there is truth in the other suggestions here, but my money is on the 2001 battery.

When the OEm AC Delcos fail (and 3-4 years is about when) you will see voltage fluctuations. This is because a failing battery builds up unpredictable internal resistances. Night driving increases the amperage through the battery making the appearance of these resistances more apparent.

Seriously, have the battery checked along with the connections, alternator and regulator. I'd start with the battery though . .

Hope you find and fix the problem before leaves you stranded.

 

You don't say how old your car is and what battery it has, but that's a place to start. If the battery's headed south all sorts of things can start to go "wrong."

Good luck.

 

i think its the original battery in the car from 2001 but that shouldnt affect voltage while running should it <-----copied from original post

in case you missed its a 2001 but im gonna replace the battery anyhow with an optima just wondering if anybody might have had any similiar problems and what to look for if they did

 

[/QUOTE]last night i was driving my car and noticed the dash lights seemed to be getting dim not much but enough to get my attention so i pull up the battery voltage and its going from 14.1 to 12.9 to 13.4 to 12.2 back and forth this was at a steady speed
[QUOTE]

You say pulled up your "battery voltage", but if you were moving with they key on, your must mean you pulled up your alternator output. If memory serves, you turn the key on without starting the engine to read the battery voltage. One reads the output of the alternator (moving) the other reads the charge on the battery (not moving, engine not running, key on).

Big difference to those who want to help troubleshoot. If you let your car sit for a while then take it out, you may be stressing the alternator. I learned that from my C4, and replaced it with a ultra-heavy-duty alternator that was modified by the Corvette Clinic in Sanford, FL. Don't know whether they have one for a C5, but if so, I will go for it.

 

I would check the alternator, esp. the voltage regulator! Mine went out on my '98 Pace Car at 50,000 miles. I was having similar problems!

 

{quote}You say pulled up your "battery voltage", but if you were moving with they key on, your must mean you pulled up your alternator output. If memory serves, you turn the key on without starting the engine to read the battery voltage. One reads the output of the alternator (moving) the other reads the charge on the battery (not moving, engine not running, key on).

Big difference to those who want to help troubleshoot. If you let your car sit for a while then take it out, you may be stressing the alternator. I learned that from my C4, and replaced it with a ultra-heavy-duty alternator that was modified by the Corvette Clinic in Sanford, FL. Don't know whether they have one for a C5, but if so, I will go for it.{quote}
the dic says battery volts anyone with common knowledge and read the post would have known that alternator ouput is being read while moving (sorta ) i had a loose positive terminal when i installed my stereo and hit a bump and everything went to nothing so it actually reads output of the alternator but disconnect the battery and it reads nothing it uses the battery as a piggybak for the alternator
however i havent drove my car for 2 days and started it this morning and the dic displayed voltage of 10.6 right after starting and then worked its way up to 14.3 after it idled down from start
i'll load test the battery and we shall see if i have any problems
ive only had the fluctuating voltage symptom one time and have driven my car several times since with no problems so i guess well see today how she does

 

Had exactly the same problem with my 2002 Coupe. Dealer suspected the battery terminals were loose and dirty. Cleaned and tightened and problem disappeared. Good place to start before you analyze the reg. etc.