Charging voltage below 14 w/stuff on??

[jfryjfry]

it looks like the days of a regulator keeping your voltage at 14v all the time are gone according to a notice/bulletin from gm i found while researching this issue, but i'm not sure if we have a problem with our new (to us) 08 tahoe.

It's always been 14v whenever i've looked at it but today, toward the end of a 20 minute drive i noticed the voltage was below and seemed to be dropping. lights on, blower motor on, wipers on, radio on.

so i got home, didn't shut it off and put a multimeter on it. it was just over 13 (can't remember exactly - like 13.1), and the truck kept it there even as i turned stuff on and off.

turning something on would briefly lower it then it would raise it back up. likewise turning something off would briefly raise it, only to be 'corrected.'

this leads me to believe the alt is actually working and the car is regulating it.

so i shut it off and restarted and it was reading 15.5ish. i didn't let it run that long. coming here, it looks like the car is really smart and i just want to know if this sounds right.

looking at the bulletin, i thought it would have read 13.8 v since so much was on.

just want to know if we have a problem and it sounds like a dealership may or may not know what they're doing.

it apparently has a new battery, too. i'm trying to contact the po to see why and maybe they had this problem before, dealer said to replace battery and it's still here.....

 

[clkelley]

Sounds to me like the alternator may be too small for the truck from the factory. But I have had a LOT of GM vehicles that actually did the same thing that I never had issues with. I haven't seen the TSB on it, but I will assure you there are dealers out there that never do a TSB lookup and wouldn't know how if you asked them.

However, I would not expect the voltage gauge to read a constant 14V, factory gauges in and of themselves are very inaccurate. For example, our Denali usually runs what looks to be 210* all the time according to the factory gauge, but when I hook the Edge Ensight up, it shows a more accurate average of 195*.

 

[jfryjfry]

thanks, and i agree about factory gauges. i checked with a dmm and got wierd results.

i didn't see the technical forum here and found more info there. sounds like this just could be normal.

gotta get used to new technology i guess. I'll be keeping an eye on it, but i no longer feel like we got a lemon.

 

[clkelley]

Yeah, I wouldn't worry too much about it. Like I said, I have had MANY Chevy trucks and almost ALL of them fluctuated like that, I have caught myself watching that gauge like an eagle in the past because the fluctuations at times seemed extreme, but I have tested enough of them to learn that I can basically forget trusting the factory gauges...lol

 

[jfryjfry]

yeah, it just seems to be normal. but it's wierd: like many guys here, i had never noticed it before. Not sure if that's just because i never happened to look while it was low or if it just started on its own.

but it seems to be doing it a lot. I guess it's just the way the computer is trying to eek out a little more mpg.

as far as trusting the gauges, it seems to be fairly accurate. but even if not, as long as it's consistent it will let me know when something changes.

 

[tonymac617]

As long as your Battery light isnt blinking on the DIC, I wouldnt worry about it. Just replaced my 130amp Alt after being stranded at the mall....$300 later for the tow and new Alt shes purring like a kitten again.

 

[sgkk67]

I have been told since 2006 that the alternator is high output and it will fluxuate like that, I have had a 2006 Tahoe z71, 2008 denali and now a 2011 tahoe ltz, all did the same thing.