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2005 Silverado Voltage Drop



I have a 2005 Silverado crew cab Z71 with 5.3L engine. I have been checking voltage issues with a Torque OBD and a voltage meter. The voltage usually runs at about 13.7v. Last year during hot weather, the voltage would drop to 12.0v and AC will blow hot air after driving 15 or 20 miles. I replaced both the alternator and battery (twice) with no improvement. With the truck running, AC blowing hot air, and voltage at 12.0v, I disconnected the alternator wire and then reconnected and the voltage immediately jumped to 13.7v and the AC will work again. I later found that I could do the same thing by pulling over, shutting the truck off for a couple seconds, and then restarting. After resetting, it might run fine for another 20 miles or just a few miles before the voltage drops again.


It is doing it again this summer (maybe in the winter too but I might not notice it). This week, thinking it could be a problem with the AC, I have been driving with the AC off and the windows down and monitored the voltage. After several miles, the voltage drops slowly from 13.7v to 11.9v with the AC off. After 20 miles or so, the voltage slowly climbs to 13.7v again.


I understand that the voltage will vary, but dropping to 12v which shuts down the AC is a problem when it is 90 degrees!


Thanks in advance.


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3 answers to this question

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Good thing is you have a crew cab! The front windows are low speed, and the front and rear windows down together is your high speed!


Sorry, had to say it because I have been doing the same thing with my truck in the "warm" Midwest weather.



I would start with checking all of your connections between the battery and alternator, most importantly the grounds.


Start with that, and see what happens. Not sure if your compressor could still cause a drag on your system, unless it is malfunctioning.

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Buy a big three kit, it contains 0/1 gauge wires to run new positive and negative wires throughout, there you can eliminate any wiring issue you might have going from the alt to the batt and the grounds too. Also, what Alt are you using? Do you have a lot of accessories you use like subwoofers, external lighting, etc???? I would upgrade to an bigger alt to see if that corrects the problem or try what I suggested above.

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