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OT 2005 GMC Alternator Question

B

Bobl1958

Well-known Member
Noticed a couple of times lately that the needle on the amp gauge is reading about 12-13amps, below the 14amp mark that it normally runs at. Usually a needle width above the 14amp mark.

Driving the other day about 4 miles from home I just happened to notice is seemed to be low. I checked it when I got home with a handheld and it showed the gauge to be correct. Shut the truck off and started it back up and it was showing just over 14amps.

Driving a couple of days later and it did the same thing. My question is would the alt be on it's way out, or does the alt back off when things are charged up. Wife drives this a lot and hate to have her get stuck somewhere because the alt went out. Any thoughts? Thanks - Bob
 
(quoted from post at 11:59:57 04/14/16) Noticed a couple of times lately that the needle on the amp gauge is reading about 12-13amps, below the 14amp mark that it normally runs at. Usually a needle width above the 14amp mark.

Driving the other day about 4 miles from home I just happened to notice is seemed to be low. I checked it when I got home with a handheld and it showed the gauge to be correct. Shut the truck off and started it back up and it was showing just over 14amps.

Driving a couple of days later and it did the same thing. My question is would the alt be on it's way out, or does the alt back off when things are charged up. Wife drives this a lot and hate to have her get stuck somewhere because the alt went out. Any thoughts? Thanks - Bob
Click to expand...
OLTS! and it isn't functioning correctly if showing 12-13 volts.
 
It would read lower if you had the a/c, headlights, or other high draw loads running. Sounds relatively normal.
At least, I think it sounds normal.
Aaron
 
Noticed my new to me '08 doing the same thing on the way home yesterday. Restarted at home and back up to 15 or so.

I just Googled it, and it seem as though it is some sort of fuel saving deal to basically shut down the alternator under certain conditions. Started in 2005 so your truck should have it and apparently is normal. There should be a section in your owners manual to explain it. I haven't read mine either.....
 
If you look at the battery cables you will notice a small amp clamp. This sensor allows the pcm to monitor the charging system and excite the alternator as needed. It is normal for the volt gauge to vary on these vehicles.
 
my 06 wt was doing that for a while, eventually the alternator gave up the ghost.when it dies, you have about 40 minutes of drive time before the truck shuts down. when the volt meter hits about 9 volts, thats all she wrote.
 
I replaced the brushes in my 2000 Chevy. They cost me $5.00 from a rebuild place. Takes longer to pull and reinstall the alt. than it does to change them.
 
Thanks for the replies. I actually meant volts..lol, but wasn't thinking. I appreciate your replies. Bob
 
I bought a 2005 Chevy Silverado 3 years ago. I replaced the alternator when I saw mine doing that-it read no charge at the battery too! When it did it again I called my Dad. He googled it-guess what-they shut the alternator off when the battery is charged! Yep, its normal for that buzzard!
 
Isn't it amazing? A person goes to the store and buys a VCR, DVD player, or a microwave oven and sits for an hour reading the manual and learning how to operate it. The same person spends $40,000 on a truck and never even cracks open the manual.

????????????????? Go figure!!
 
Don't trust the dash reading the dashes in those trucks are known to be junk and mine reads all the way to the right at the moment. Check it with a multimeter then turn on everything and check it again.
 
omahagreg has it. The alternators in 2000 or so and newer GM trucks are computer controlled. When the computer decides the battery is fully charged it shuts off the alternator. Supposed to save fuel and overcharging the battery.
 
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