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Discussion Starter · #1 · (Edited)
Since last years I have been chasing some fault codes, and it only happens when the outside temp is around 90's.
The battery was already about 5 years old and the voltage was not maintaining, the alternator was charging good so I replaced the battery and no codes.
Here we go again, the little Gremlin of codes and this time the codes are:
P0700 - CONFIRMED
U0073 - CONFIRMED
U0100 - CONFIRMED
P0700 - PENDING
U0073 - PENDING
U0101 - PENDING
U0100 - PENDING
U0073 - PERMANENT
U-100 - PERMANENT
This time I checked the charging system with my Fluke meter and found the alternator is charging very low at 12.52v and yet the battery indicator light was just lightly above the voltage threshold level. This only happens when temp is above high 80's the radio is on, the AC is on, the fan blower is set at medium, and the SUV is just coming to a stop.
the Foxwell scan tool voltage was showing 12.20v, the graph was showing from 12.17v to 12.28v
So now what I need to do is to replace the alternator, and confirm the output voltage is at least 13.50v or better
 

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Normal charging for your vehicle from the GM Repair Manual is 13.8 to 15.5 volts.
This depends on load, temp, battery charge, current sensor on the neg cable, BCM, etc etc.
If you suspect a bad alternator, increase the load by turning on headlights, A/C fan on high, power windows, etc and watch your voltmeter.

A bad alternator is a possibility and probably a good place to start, it could be wiring, BCM, battery current sensor, battery cables, serpentine belt or another thing.
 

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Discussion Starter · #3 ·
Normal charging for your vehicle from the GM Repair Manual is 13.8 to 15.5 volts.
This depends on load, temp, battery charge, current sensor on the neg cable, BCM, etc etc.
If you suspect a bad alternator, increase the load by turning on headlights, A/C fan on high, power windows, etc and watch your voltmeter.

A bad alternator is a possibility and probably a good place to start, it could be wiring, BCM, battery current sensor, battery cables, serpentine belt or another thing.
Thanks for the fast reply, and I did load everything and that's how I got the 12.50 idle voltage.
Is there a fuse link for the alternator or just a fuse box fuse?
 

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Discussion Starter · #4 ·
Okay, I just checked the charging system with the engine being cold at start up, and the voltage from the battery post is 13.64v, while the alternator post voltage is 14.13v. These reading are from having the AC on, fan on high, headlights on with high beam on, and radio on.
The differences between both readings is just 0.49v
Yesterday outside temp was close to 93* AC on, fan on medium, radio on and the voltage was 12.50.
Would you thing the alternator's insulation is breaking down with high outside temp?
During the winter time I had no issue with any codes or voltage, only when the outside temp is around 90's is when I start to develop these voltage problems.
Any thoughts would be appreciated
 

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Would you thing the alternator's insulation is breaking down with high outside temp?
I would think a bad diode is more likely.
Is there an auto parts store like Auto Zone in your area that can test your alternator?

Fuse number 28, underhood fuse block, is the only fuse for charging other than the big 200 amp one.
This is one of your BCM fuses.
 

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Discussion Starter · #6 ·
I would think a bad diode is more likely.
Is there an auto parts store like Auto Zone in your area that can test your alternator?

Fuse number 28, underhood fuse block, is the only fuse for charging other than the big 200 amp one.
This is one of your BCM fuses.
I'll let you know the outcome when the alternator replacement comes in and install.
Thanks
 

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Discussion Starter · #7 · (Edited)
I finally installed the Alternator replacement, and let me tell you something, that is not an easy job, as It took me about 7 hours to do.
After the installation the voltage readings were between 14.5v - 14.75v with AC on fan on low, engine idle
After turning everything on including high beams the voltage was around 13.0v engine on drive not park.
I thing I still have an issue since the Service Stabilitrak come on for a second and disappear.
After doing many research many have different Service Stabilitrak faults from spark plus to wheel hub unit. I'll check the code and se what it claimed to be
 
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