battery light on

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Spish

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So my battery light on the dash came on yesterday, still starts great and don't notice any thing wrong, what could cause that? I did my timing belt a few weeks ago, might have the alternator belt too tight? How do you check the belt tension?
 
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Your alternator might be pooping on you. But before you get excited about getting a new alternator, check the connections on the battery. The battery light is on because the battery isn't maintaining a charge that the computer wants it at.
I had a situation with a race car long ago. Be it that it was a race car I rigged up a lot of stuff, one of which was using a smaller battery and thus rigged up a new positive cable. Apparently I did a crappy job at it and the battery wasn't getting a good connection from the positive cable. Long story short, I was driving one day and saw the battery light come on, thought nothing of it, then it flickered and one day while on the interstate the car just pooped on me. Problem bad connection to the battery.
 
bad alternator (brushes, internal regulator, rectifier set, short/open windings), loose belt, bad battery cables, bad alternator wiring/connections, loose/missing grounds.

A little systematic trouble shooting is required, but cleaning and tightening battery terminals (also clean battery top if it needs it) and the grounds at fender wall, alternator, and the one on engine by diagnostic plug are are good ideas anyway. See if you have charging voltage at the battery terminals of 14-15V. Verify state of charge of battery to see if it is going down--should be 12V-12.5+V with engine off. Also check alternator fusible link in engine junction box. That's how I'd start.

Don't ignore it. Battery will keep car running and starting for a short time (at night, less than 30 minutes) until it decides to crump at worst possible time: miles from home, at night, with wipers on due to rain or snow.
 
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RAB said:
The battery light is on because the battery isn't maintaining a charge that the computer wants it at.
Click to expand...

This is not precisely true. The light indicates that the battery is discharging rather than charging or doing nothing. If the motor is running and the alternator is producing current, the battery should be receiving a charge, not discharging. It can be fully charged but show a warning light because the alternator is not supplying voltage to the car. The computer isn't even in the warning light circuit, the signal comes straight from the alternator's voltage regulator.

Charging circuit diagram (Factory Wiring Manual)
 
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TheDurk said:
This is not precisely true. The light indicates that the battery is discharging rather than charging or doing nothing. If the motor is running and the alternator is producing current, the battery should be receiving a charge, not discharging. It can be fully charged but show a warning light because the alternator is not supplying voltage to the car. The computer isn't even in the warning light circuit, the signal comes straight from the alternator's voltage regulator.

Charging circuit diagram (Factory Wiring Manual)
Click to expand...
Excellent, thanks for clarifying.
 
Check it out asap - if it's a dead or dying alternator it can kill the battery along with it if you leave things too long - a bad battery can similarly put excessive demands on your alternator and lead to early failure of that also.
 
Looks like it is my alternator, I put a voltmeter on the battery with the engine off and had 12V, started it and it didn't go up. Looks like I have a valve cover leak and the oil might have fouled the alternator brushes, anyone have any idea what I could try to clean it with? The alternator is only about 1 year old.
 
Do you have a warranty on it? and I know when you get mud in there you can ussually just rinse it out with a water hose i dont know if that will work for this though.

Let me know what else you come up with becuase mine just came on today after I put in my new HID headlights and used my lights on my rack for about an hour tonight. So I'm interested in to see why it did that.
 
First, I would recommend you take the alt. to a shop that can bench test it for you. This eliminates any possibility the fault is in the on-board wiring. If you settle for a test with it on the motor, make sure they connect right to the alt. Some of these auto-parts stores don't and then try and sell you a new alt when all you needed was a cable. Don't fall into the trap of buying a cheap reman and turning in your stock Denso for core. Try and fix it yourself or get someone to repair it. The after-market and remans probably won't last as long as a repaired Denso.
 
TheDurk said:
First, I would recommend you take the alt. to a shop that can bench test it for you. This eliminates any possibility the fault is in the on-board wiring. If you settle for a test with it on the motor, make sure they connect right to the alt. Some of these auto-parts stores don't and then try and sell you a new alt when all you needed was a cable. Don't fall into the trap of buying a cheap reman and turning in your stock Denso for core. Try and fix it yourself or get someone to repair it. The after-market and remans probably won't last as long as a repaired Denso.
Click to expand...

I put the voltmeter off the terminal on the alternator and got about 11.5V, so I think its putting out enough to keep the battery just charged enough, but low enough to turn the battery light on.
 
Spish said:
I put the voltmeter off the terminal on the alternator and got about 11.5V, so I think its putting out enough to keep the battery just charged enough...
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I doubt it. You are pretty close to toast at 11.5V.

voltchart1.gif



How cold is it there? Be careful or that battery may freeze on you--I heard about some low temps at night in AZ.
 
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Just used some CRC electrocleaner on the alternator and cleaned all the terminals, only getting 11.7 before starting and goes down to 11.5 after start up. Getting the same number when checking the terminal off the alternator. Guess I'll take it out and get it bench checked. Thanks for all the info guys!
 
Maybe you can help me troubleshoot my issue too. Two days ago the ABS and battery light came on. The battery light would flicker, go out, come on but the ABS stayed on. Used the multi meter and had 12v with engine running, 10v off. Bought a rebuilt denso 80A alternator and replaced the old one tonight. The ABS light is now off but the battery light is on constantly. Testing again with my meter, i get 10v. So i took it to advanced auto for a warranty check and their meter tests it at 12.42v engine off and 14.6v running. My read is the battery is below 80% charge. They tell me they wont replace the battery yet.

Battery is an Optima Red top bought in 4/2012

So did my alternator kill my battery? Will my alternator eventually charge up the battery again? Truck runs great.
 
DrCoffee, do you have an update?

I have the same problem, (have not changed alternator, multiple sources tell me it's ok)

Thanks in advance!
 
I found the problem with my rig. There are three wires that connect the alternator. The white wire in the harness that monitors the battery voltage and tells the alternator to maintain voltage had a small nick in the plastic wire coating from the factory. Over time it corroded through and broke. So my alternator was running at full power perpetually. It also dropped my mpg to 17 because of the drag on the motor.

Check the continuity and voltage of each of the alternator harness wires. Mine is probably a unique situation but you never know.

In the end, I replaced the alternator, fixed the wire and kept the battery.
 
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Update for me as well.....

Two days after I posted here I started seeing the gauges start going crazy (as others reported in other threads too with the battery light and/or ABS light) So, The alternator has been replaced and the issue is resolved. Sort of.

Looks like I have a valve cover gasket leak left front side that eventually is falling onto the alternator. Which would explain if it shorted the windings.

But as you know, it takes removal of the intake manifold to replace the valve cover gaskets. And with 295,000 miles, (I bought it new in 1996 :clap2: ) i'm just going to let it slide for now.
 
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