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Amedee
Amedee, Former ASE Master Tech
Category: Car
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Experience:  ASE certified tech advanced level specialist. Wisconsin certified emissions state inspector
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04 mazda 6 battery light on. Alternator not charging.

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04 mazda 6 battery light on. Alternator not charging.

Hello!

 

With the alternator unplugged and the engine running, one of the wires from the PCM will have a 12 volt reference on it and when plugged in that circuit turns to about a 1.5 volt square wave signal that is used as a feedback from the alternator to the PCM. The other wire at the alternator will show very little voltage when the alternator is unplugged and the engine is running and then turns to about a 10 volt square wave when the alternator is plugged in, this is the command circuit for the PCM to tell the alternator to charge.

Customer: replied 7 years ago.
I will check the alt. with the Snap-on vantage and email you back.
Chris

SOunds good!

 

Be sure that all of the inputs are correct going into the back of the alternator with the key on.

Customer: replied 7 years ago.
Checked the wires from alternator. One wire has the 12 volt reference but not seeing the 1.5 square wave signal. The other wire does have very little voltage unplugged then a 10 volt square when plugged in.
DO you need a wiring diagram?
Customer: replied 7 years ago.
I have one.

You will need to check for this square wave from with a lab scope.

If all the inputs are correct, then the new alternator is bad and will need to be replaced.

 

 

Customer: replied 7 years ago.
I have the Snap-on Vantage. I did not lower the range when checking for the 1.5 volt wave.
So you did not check for this square wave form... is that what you are syaing?
Customer: replied 7 years ago.
I did check but the range was to high I just need to lower the range of voltage.
Customer: replied 7 years ago.
When the alternator is charging there is a 1.5 wave form. When the alternator stops charging I lose the wave form.
There is a lot of problems with rebuilt alternators on these vehicles. I think we just have a bad new alternator. With the alternator disconnected and the engine running, one of the wires from the PCM will have a 12 volt reference on it and when plugged in that circuit turns to about a 1.5 volt square wave signal that is used as a feedback from the alternator to the PCM. The other wire at the alternator will show very little voltage when the alternator is unplugged and the engine is running and then turns to about a 10 volt square wave when the alternator is plugged in, this is the command circuit for the PCM to tell the alternator to charge. If this circuit is present, the computer is doing its job. If the 1.5 volt square wave from drops off, this means the alternator is bad. Just be sure to check these signals at about the same time. Be sure the 10 volt square wave from is present, as well as battery voltage (on the other wire) to the back to the alternator when the alternator is not charging.
Customer: replied 7 years ago.
We are going to warranty out the alternator I will let you know how it goes.
Sounds good!

I hope this helps. You can always accept my answer now, and repost back again later on if you have any more questions. If you want to discuss it some more just hit "reply", it's free to do so otherwise don't forget to hit "accept" and leave positive feedback if you found my answer helpful.

Regards

AMEDEE
Customer: replied 7 years ago.
I will.
OK
Amedee and 5 other Car Specialists are ready to help you
Customer: replied 7 years ago.
So far so good. Before the alternator would stop charging about 20 min. after start up. Ran for 30 min. yesterday and then the boss drove it home. No light and still charging. Thanks for the help!