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Cam I'm having the same issues with my alternator not

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charging battery. I disconnected the...
Cam I'm having the same issues with my alternator not charging battery. I disconnected the negative side and reconnected it. It started charging then after 5 minutes it started with the same issues.
Submitted: 4 months ago.Category: Chevy
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Answered in 1 minute by:
12/18/2017
Chevy Mechanic: Pete, Auto Service Technician replied 4 months ago
Pete
Pete, Auto Service Technician
Category: Chevy
Satisfied Customers: 31,730
Experience: 14 years GM dealer Technician.
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Hi my name is ***** ***** I will be happy to assist with this today.In some cases I may need more info to assist better.I apologize for any delay.

Has anything been tested or replaced to try and locate or repair this fault here at all?

Let me know,thanks Pete.

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Customer reply replied 4 months ago
No. I had a o2 fault bank one and I replaced the o2 sensor but this problem started before I replaced it
Chevy Mechanic: Pete, Auto Service Technician replied 4 months ago

When you say you disconnected the negative side was this the negative cable you disconnect and reconnect?

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Customer reply replied 4 months ago
I also pulled the plug on the alternator and checked with the test light the three leaves going to the connector and I have no power
Chevy Mechanic: Pete, Auto Service Technician replied 4 months ago

Have you tested the actual voltage output at the alternator power post itself when this occurs to see if a charge signal is coming off of it?

Let me know,thanks Pete

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Customer reply replied 4 months ago
I have when the car was charging I was getting the 14 volts coming out to the battery itself I've taken the alternator off and took it in and had it tested and it passed when I don't get the power I checked the plug and there's no power there
Chevy Mechanic: Pete, Auto Service Technician replied 4 months ago

O.k., the power source or signal control comes from the PCM ( engine and transmission computer ).The PCM has been known to cause this type of fault here as it can intermittent fail to send the signals to the alternator to tell it to charge.I have had to replace and program the PCM in the past before for this type of fault here.Unfortunately, it isn't like the older systems where the alternator charge control ran off of the instrument cluster and a fuse.It is controlled by the PCM instead.When you do the battery disconnect and reconnect you are actually resetting the PCM to allow it to work and charge again.

If more help is needed, use the reply tab to continue our conversation. If no further assistance is needed, kindly rate my service, your 5-star rating is appreciated ( should be a link to click on here or above).You can rate at any time and we can continue to work on your question as this will not close out your question.I work on delivering the best answer and help here but in some cases, it can be difficult to do without seeing the vehicle.

Thanks Pete

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Customer reply replied 4 months ago
is there a way to test the pcm?
Chevy Mechanic: Pete, Auto Service Technician replied 4 months ago

Do you have any voltage or ground signals on the gray wire at the alternator when it is charging?

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Customer reply replied 4 months ago
No grey wire. White,brown, blue
Chevy Mechanic: Pete, Auto Service Technician replied 4 months ago

O.k.,the white one may be gray just color changed under heat from the engine over time.I have seen that occur before.This wire, does it have a power or ground signal on it when the alternator is charging and when it isnt charging does this wire lose the power or ground signal?

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Customer reply replied 4 months ago
Now I can't get it to charge again
Customer reply replied 4 months ago
Is there any way by removing the PCM to take it somewhere to get tested? Also after I purchase a new PCM how do I program it
Chevy Mechanic: Pete, Auto Service Technician replied 4 months ago

Unfortunately the only place that could test it is an online repair center by sending it to them for testing.

If it needs replaced then it has to be programmed by either a dealer or someone who has access to GM programming as unfortunately this is the only way it can be done.

Let me know if you need anything else and feel free to rate my help here or above ( should be a link to click on ) as this is how I receive credit for my time,this can be done at any time and you can still come back here and reply if needed.Your 5 star rating is appreciated

Thanks Pete

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Customer reply replied 3 months ago
Pete it is not the computer installed a new one and still no charge
Chevy Mechanic: Pete, Auto Service Technician replied 3 months ago

Was the wiring checked leading from the computer to the alternator at all?

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Customer reply replied 3 months ago
there is continuity between the wires from the PCM to the alternator
Chevy Mechanic: Pete, Auto Service Technician replied 3 months ago

That is odd.With what you have going on here it sounded like the PCM or wiring at fault.

The only other thing I see here is an internal fault in the alternator intermittently causing this issue with it needing to be replaced.Everything else has been covered and is o.k. or was replaced.It is very possible the alternator is acting up internally intermittently creating this fault here.The only way to know for sure is to have it tested on the vehicle when it is acting up at a local shop or parts store.

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Customer reply replied 3 months ago
When I replace the PCM I unplugged the three wires going to the alternator and I check them with a test light and there was no power going to them. But when I unplug the wires I went to the number 15 on the green plug and the gray wire there was continuity number 75 and the brown wire and there was continuity so not sure why no power is being sent out
Chevy Mechanic: Pete, Auto Service Technician replied 3 months ago

Are you saying there is continuity between 2 different wires leading from the PCM with the alternator unplugged?

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Customer reply replied 3 months ago
No. Two separate wires
Chevy Mechanic: Pete, Auto Service Technician replied 3 months ago

And you have no charge directly at the red wire on the alternator is this correct?

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Customer reply replied 3 months ago
Correct
Chevy Mechanic: Pete, Auto Service Technician replied 3 months ago

This is odd you have no signal to charge.I am going to post the charging system test procedure below.The only thing I can suggest here is to follow this procedure to see what it says needs replaced or repaired for this issue.You will need a special tool though unfortunately and I have located one for sale below in the link:

https://www.ebay.com/i/391935609896?chn=ps

Here is the testing procedure.

https://www.dropbox.com/s/q7hwm6ne3f1cr0e/1-12-26.png?dl=0

https://www.dropbox.com/s/odil6s3hc8ag52c/2-12-26.png?dl=0

https://www.dropbox.com/s/fw06u6n7us68usu/3-12-26.png?dl=0

https://www.dropbox.com/s/xjrtxt6p187g2i4/4-12-26.png?dl=0

https://www.dropbox.com/s/7k2y7ziyhduuead/5-12-26.png?dl=0

https://www.dropbox.com/s/rpsowck4hwhxw38/6-12-26.png?dl=0

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Chevy Mechanic: Pete, Auto Service Technician replied 3 months ago

Hi, just checking in to see how things are going. Do you need further assistance?

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Pete
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Experience: 14 years GM dealer Technician.

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