Help! battery or alternator???

**ct1.8t4me** · 05-24-2008 07:22 AM

I'm posting from my phone...my battery indicator light went on this morning. When I first turn the car on, the volt gauge goes to the normal position around 14 or whatever, but after a minute or so it drops to exactly 12. So I'm a little confused - I don't know if this is an automatic behavior where it goes from showing the alternator output to the battery output if there is a problem or what. Any ideas? The battery is at least 5 years old if that matters. If anyone has any idea - could you respond to [email protected] as that goes straight to my phone. Thanks guys - I'll post the resolution here when it's figured out.

**Seerlah** · 05-24-2008 07:54 AM

The battery light comes on as soon as voltage drops below 12 volts. Normally, your battery holds a charge of a little over 12 volts. When the car is running, you should have a little over 14 volts.

To test your battery, you can go to Autozone and have them do a test to see how much charge your battery is holding or you can simple get a volt meter and do it yourself. You should have ~12 volts (not below 12 volts) with the car off. To test the alternator, you can maybe:

1. turn on the car
2. sit idle with no electronics on or foot on gas
3. turn heat or couple of high voltage components that would normally take a good amount of power to operate
4. pay attention to the battery volt meter built into the dash to see how it sits.

If it drops down very fast as due to your electronics being used, turn off the electronics immediately. Your alternaotor is shot. You can still run your car on the battery (depending on how much voltage it is holding), but only to the shop to get your alternator replaced. And you should not need a new battery.

**njm23** · 05-24-2008 08:51 AM

get a voltmeter and test it yourself in 2 seconds.. battery should put out around 12-12.5 and alternator should put lut around 14 or so.. You'll find out which one is bad pretty quick.

**ct1.8t4me** · 05-25-2008 03:27 PM

If i test the battery terminals when the car is running should I get 14 volts or 12?

The problem gets worse now - it has become intermittent. The light will come on and the volt meter will drop to around 12 - then I'll go over a bump or something and it will go out and the swing back up to 14ish.

Has anyone had an alternator get flaky like this? Or am I looking at connections now? Where are the grounds? I see the one by the battery - where else?

**creechsa4** · 05-25-2008 03:32 PM

14 volts car on, leads directly on posts. cleaning grounds is always necessary and good preventative maintenance.

**Toyotatech** · 05-25-2008 03:40 PM

Most voltage lights come on because the alt. is not working right. Start the car let it idle, and remove the battery with the car running. If the car shuts off the alt. is bad otherwise if the car stays running the alt. is good.

**ct1.8t4me** · 05-25-2008 03:41 PM

OK - I was able to test the battery voltage when the car was on and the indicator was on and voltage at the battery was 11.8 - so I guess that narrows it down to either the alternator or the connections somewhere. Is there an easy way to narrow it down to either one? I suppose if I could get straight to the output of the alternator I should be able to see 14 volts. Any info on the specific posts to check? I can't really see anything back there.

**njm23** · 05-25-2008 05:57 PM

Just check our alternator with a volt meter.. Ground it out on one of the bolts holding it, there is a little black cover on the back you can take off and use that for the +. As far as grounds, you check all your wiring, check the starter grounds (this was my issue when my alternator wasnt charging the battery). But you will no if the alternator is bad when you test it directly. If its good check all your grounds,.

**ct1.8t4me** · 05-25-2008 06:57 PM

Thanks guys - I'll check it out tomorrow.

**Udo** · 05-25-2008 10:21 PM

Originally Posted by Toyotatech

Most voltage lights come on because the alt. is not working right. Start the car let it idle, and remove the battery with the car running. If the car shuts off the alt. is bad otherwise if the car stays running the alt. is good.

that would work, but really not recommended on newer cars

**calitri808** · 05-25-2008 10:34 PM

battery light on, most likely your alternator

**Toyotatech** · 05-26-2008 01:43 PM

Originally Posted by Udo

that would work, but really not recommended on newer cars

Go back to school son.
Let me ask you, what are you doing when you jump start a car? A dead battery is just like having no battery. Batteries start cars alternators provide power.

**InTTruder** · 05-26-2008 01:52 PM

NO alternator = no charging of battery.

Having replaced a battery, then alternator, your symptoms "sound" as if your alternator is failing or has failed.