Charging Voltage low?

[JuggaloJeff]

My car is:

1998 contour SE 5 speed
135,000 miles

Ive had the car for 4 years now and haven't had that many problems, just normal stuff, replace things here and there.

Now earlier today my battery light came on and would go off and then back on every now and again(sometimes around turns.)

The battery is pretty new, bought it 3-4 months ago...its a duralast

Now the alternator was replaced back in 2005, however I did not replace the battery @ the time as it tested out fine although of course it was recommended.

Now I got home and checked the electrolyte levels and those are fine, and the battery clamps and everything visible is tight on the battery, then I hooked up a voltmeter and its 12.5 or so @ rest as normal but then with the car running its around 12.1, so how can that be, is it not charging or undercharging? Could it be the drive belt, since I have owned the car I haven't had the belt changed

 

[Ray]

It "could" be the belt, sure.. you could check the tension of the belt itself.
(try to rotate the belt while on all the tensioners/pullies and you should get no more than 90º. push "in" on the belt and you should get about 1/4" of movement.

You could also check for loose/wobbly tensioners/pullies. (remove the belt by releasing the tensioner with a 3/8 drive breaker bar and then wiggle/spin the accessory drive pullies, etc)

It could also be the alternator..

with the voltage test you performed already, it eliminates the battery and thus you could either replace the alternator, or inspect the mega-fuse (located against the firewall, under the spark plug coil-pack (where all 6 plugs lead to and plug in) The mega fuse is also noted in the alternator how-to above.. test with a multimeter for near infinite resistance.

I suspect either the mega-fuse or the alternator.

 

[Dyoel182]

but it could just be the voltage regulator thats mounted on it.

Many times the reman. alternators fail faster than the OEM alternators. It could be the voltage regulator built in to the alternator.

(apologies for the accidental removal of post. Reconstructed by memory, please edit to re-state more appropriately..)

 

[Ray]

Which, in this case, means pulling the alternator to get to it either way, unless you want to go through a ton of work to get the VR off the alternator while still on the car.

 

[SVT_CT]

...or inspect the mega-fuse...test with a multimeter for near infinite resistance...

Just to clarify what Ray said above, near infinite resistance indicates a bad megafuse. A good one will have zero ohms or close to it (within a couple ohms).

 

[Ray]

oh... d'oh.. I guess that didn't sound too clear..

Thanks for the follow-up correction.

 

[projectSHO89]

Just to clarify what Ray said above, near infinite resistance indicates a bad megafuse. A good one will have zero ohms or close to it (within a couple ohms).

Well, actually, a good fuse will have as close to zero resistance as is possible and should measure that within the limits of the ohmmeter.

Even a small fraction of an ohm's resistance in a high current circuit will cause a substantial drop in voltage across it. As an example, 1/10th of one ohm in a 12V circuit trying to pull 12 amps will drop 1 volt across the resistance. 1/2 an ohm will drop 4 volts.

I'd be the alternator/regulator is bad.

Steve

 

[iskoos]

If you don't find anything after checking that fuse, pull out the alternator and get it tested at autozone/autoparts store.
Removing the alternator is not very simple but doable. Having done that 4 times so far(I am on my 4th alternator) I believe I can do it in 45 minutes.
I think messing with voltage regulator will not worth it.
Keep us posted...

 

[Dyoel182]

You know they can do a basic charging system test while its still in the car and tell you what the voltage is doing.