Voltage Drop at Stoplights

[TheNiceLips]

Hey all,

I've got a 1999 SE, with just over 40k miles. Ever since I got Bonnie I've always noticed on the dash the voltmeter indicates a drop in voltage at stoplights. A year ago, I replaced the battery because it was dead/factory battery. Now, a year later, I'm seeing the same issues at a stoplight, only now the voltmeter indicates that it goes <10 volts/red zone (it used to only go down to 10 volts, and stay there). I understand that the alternator isn't producing much power at stoplights because of the engine speed. But, even when I'm cruising down the highway, it'll barely get above ~11 volts, and as soon as I come to a stop, it'll go back down <10 volts. I'm just wondering: is this an alternator issue or a battery issue? Or something completely unrelated? Or maybe even normal operation? Thanks in advance.

[AJT2004]

Likely a faulty alternator- voltage at idle (without load) should be around 13-14. But you need to Confirm voltage with a digital multimeter as dash gauges can and will fail. I'm suspect because with the low readings you mention your battery is not receiving a proper charge and should have left you with a no-crank problem by now.

[reb]

I'm pretty sure Autozone can test your charging system for free and determine if your alternator is bad. Sear Auto Centers will probably also do that for you. Other places as well- no need for guess work here. Alternator is a relatively easy DIY fix.

[Bugsi]

If the alternator is fine, carefully inspect your battery cables. Typically, the positive cable corrodes inside the cable insulation. The only way you can inspect this is to cut a slit down the insulation and peel it away from the cable. If you don't find any corrosion, you can close up the slit insulation and wrap it with electrical tape to cover the slit.

I had the positive cable corrode in all five Pontiacs I've owned. They exhibited similar symptoms to what you described.

If you do have a corroded cable, I recommend getting a factory replacement from a dealer.