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Sandwich

Pig my fish!
Staff member
May 23, 2002
16,149
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01776
Since this is Carproblemsmonkey...

My wife's Elantra won't start. I've previously removed the battery and took it to THE ZONE and they recharged it, as it was dead, and then tested it, and said it was good. The car started right up and ran fine for a month since then. Yesterday, she didn't drive it, and now it's dead again.

Is it fair to assume that it's probably the alternator that's gone bad? What other obvious things can I try? The start problem is clearly from the battery, and not the starter side. It'll wub...wub..wuuub...vrooom, just like you'd expect a weak battery to do.
 

kickstand

Turbo Monkey
Sep 18, 2009
3,445
392
Fenton, MI
Since this is Carproblemsmonkey...

My wife's Elantra won't start. I've previously removed the battery and took it to THE ZONE and they recharged it, as it was dead, and then tested it, and said it was good. The car started right up and ran fine for a month since then. Yesterday, she didn't drive it, and now it's dead again.

Is it fair to assume that it's probably the alternator that's gone bad? What other obvious things can I try? The start problem is clearly from the battery, and not the starter side. It'll wub...wub..wuuub...vrooom, just like you'd expect a weak battery to do.
Yup, either the alternator is bad (have it tested) or the battery is dead/old enough to no longer hold a solid charge from the alternator
 

DirtyMike

Turbo Fluffer
Aug 8, 2005
14,288
874
My own world inside my head
If it is going a full month without the problem I think you may be leaning towards something else.

Yes defnetly start with an alternator test to make sure it is good, output and diodes, but with the symptoms I am more suspect that you have something staying on from time to time, a trunk light, something in the radio ETC....

Oh, if the diodes short they will not drain the battery, they will ruin the battery while it is running, also add to that list the every piece of electronics int he vehicle. The diodes will not do ANYTHING when the vehicle is off.....
 

eaterofdog

ass grabber
Sep 8, 2006
6,843
22
Central Florida
I'm standing by my statement, the diodes can slowly drain the battery when the car is off. This is pretty well known.

Many places will only test the alt output, make sure they check the diodes.
 

Sandwich

Pig my fish!
Staff member
May 23, 2002
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i plan on taking the alternator and the battery to THE ZONE for a test. I assume, when they bench test it, they'll make sure it's good? I don't want to GET IN THE ZONE then find out they didn't test a thing that does stuff.

I'm not sure it's been a full month. It's been a while, and they fully charged the battery and the electronics all work, so I believe it's gotta be a very slow drain, or it would be dead in another night. Electronics don't run long on battery alone.
 

DirtyMike

Turbo Fluffer
Aug 8, 2005
14,288
874
My own world inside my head
I'm standing by my statement, the diodes can slowly drain the battery when the car is off. This is pretty well known.

Many places will only test the alt output, make sure they check the diodes.

No, they will not.......... They will not drain the battery when it is not running, they do absolutely nothing when the alternator is not moving. They are just a rectifier bridge to conver ac to dc, when the armature is not moving they do nothing....... This is actually pretty well known for how an alternator works...... the other is a pretty well known misconception as to what is going on in the alternator.......

Do not get me wrong, they are in fact very important so you are on the right track to make sure they are good, make no mistake that most every testing unit that tests an alternator automatically tests the diodes while performing the load test....... The diodes can also be easily checked with a volt meter... set your volt meter to AC and check the running voltage at the battery..... no more than .250 ac volts, if more than that diodes are bad...........

If the diodes are so bad that they actually cook and short to ground...... the vehicles computer system would have failed a long time before that from the switching polarity coming out of the alternator.........

Read the actual wiring diagram, it makes sense what I am saying....
 

DirtyMike

Turbo Fluffer
Aug 8, 2005
14,288
874
My own world inside my head
i plan on taking the alternator and the battery to THE ZONE for a test. I assume, when they bench test it, they'll make sure it's good? I don't want to GET IN THE ZONE then find out they didn't test a thing that does stuff.

I'm not sure it's been a full month. It's been a while, and they fully charged the battery and the electronics all work, so I believe it's gotta be a very slow drain, or it would be dead in another night. Electronics don't run long on battery alone.
Well something like a radio amp staying on will drain a batery in a night or two, and if it is staying on intermitandly that would explain it, or a door switch staying on sometimes too..... Better way to test the alternator is int he vehicle, the az bench machine will not give it a proper load test without a battery attached in the system, nor does their system check the diodes. My suggestion for that is to get the battery charged up and drive the vehicle to a shop that can properly load test the system, it will tell you substantially more of what is going on.
in the vehicle is the only way you will get all three aspects tested properly, voltage, amperage, and diode's
 

kazlx

Patches O'Houlihan
Aug 7, 2006
6,693
1,531
Tustin, CA
The other thing you can do is pull the fuses and check amperage draw on each circuit which might help identify where your issue is. Shouldn't take more than 30 min if you have an ammeter.
 

Sandwich

Pig my fish!
Staff member
May 23, 2002
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Whell, spent the three effin hours taking the alternator out, only to have them tell me it's fine. It must be a draw somewhere. I was really hoping this car would last another year...I don't have the testing equipment to check each circuit, so the next stop might just be the shop.
 

kazlx

Patches O'Houlihan
Aug 7, 2006
6,693
1,531
Tustin, CA
You can buy a multimeter anywhere.

http://www.sears.com/shc/s/p_10153_12605_03482139000P

Pull the fuses, set the meter for amperage and stick the probes where the fuse would go. With the car off, they should all read zero or close to it. If you find one pulling even low amperage, start checking things in that circuit.

or take it to a shop and write a check for them to do it.

Automotive stuff isn't brain surgery.
 

DirtyMike

Turbo Fluffer
Aug 8, 2005
14,288
874
My own world inside my head
Whell, spent the three effin hours taking the alternator out, only to have them tell me it's fine. It must be a draw somewhere. I was really hoping this car would last another year...I don't have the testing equipment to check each circuit, so the next stop might just be the shop.
Hate being the one to say it, but unfortunatly removing the alternator to test it just took up time, you may find that the alternator is still bad in the long run... You just cannot load test an alternator properly out of the vehicle..........

BUT.......



The other thing you can do is pull the fuses and check amperage draw on each circuit which might help identify where your issue is. Shouldn't take more than 30 min if you have an ammeter.
This...... If its a draw this is how to find it right here.... it really is pretty easy to do..... If you need details on exatly how to do it I will go into them.... Digital meters work best for this.