2010 Avalanche 5.3 Ltr Alternator Voltage swings between 14.2 and 12.8

[JerryL]

I own a 2010 Avalanche with a towing package and a 5.3 Ltr v-8.    I love the vehicle.   I noticed lately that the voltage gauge on my dash shows 1 bit over 14 volts when I start it up and then after maybe 10 miles of driving, it slowly drops off to 12.8 volts.    I have had an auto parts store put a tester on the battery and they said it was good.     They also loaded down the alternator from the battery posts as well and the alternator produced 14.4 volts.

 

If while the dash voltmeter shows 12.8 I shut the engine off and immediately start it, the voltage shows 14+ volts and starts the process all over again.     

 

I never noticed this before.   Do I possibly have this in "towing Mode"?   

I replaced the belt and tensioner pulley but voltage drop was confirmed with a good voltmeter at the battery.

 

I do have the engine package that switches between 4-8 cylinders.

Whether I am in 4 or 8 cylinder mode, it seems to make no difference on the voltage drop...

 

It can run for days fixed on the 14 volt reading and then like this morning, drops off the 12.8.

I did notice that it was coming back up to 14 after being fixed at the 12 volt voltage.

 

Should the voltage swing like this or do I have a regulator going bad.?

 

Any help would be appreciated..  

Jerry 

 

 

[swathdiver]

Normal, your truck is equipped with Regulator Voltage Control and Electronic Power Management.  It's like a smart charger for your battery.  Makes them last longer.  If it stays at full power all the time, that might mean your battery is not up to task, a bi-directional scan tool can see what the battery's state of charge is.  A bad cell in a good battery can cause all kinds of gremlins, including escaping detection!

 

 

 

[richard wysong]

does it drop lower if you put a load on it such as high blower etc? I would check the battery connections, its possible the resistance increases as they heat up. also do a voltage drop test between the battery and engine and body grounds while its doing it and the same between the alternator and the battery if all that checks out you may have a regulator problem or a battery on its way out. keep in mind that alternator output varies depending on ambient temperature but should be at least 13 v

[JerryL]

Thank you.   I'm familiar with checking for voltage drop across connections due to resistance issues, so I'll start there.

 

I'll also check connections at the battery terminals as well at the output of the alternator.     

 

Jerry

[EightTrackHits]

As Swathdiver said, what you are seeing is likely normal. 

A good description of the charging system can be found in this post from an Avalanche club.

 

https://www.chevyavalanchefanclub.com/cafcna/index.php?threads/lights-flicker.52489/

The checks that Richard mentioned are worth doing if you begin to have problems, but you may be okay.  Read the description of the charging system and see if it jives with your symptoms.

 

But please let us know how it goes.

[dna9656]

A- Are all the old school trouble shooting symptoms obsolete? If I'm reading this right it's seems normal, the battery charges a little after a draw like starting the the truck... this is what i see but the management system seems to toss all the old school symptoms out....

[EightTrackHits]

The old school trouble shooting techniques are good- when you know you have a problem that OBDII can’t help you with or isn’t helping you with.  But old school thought on the new systems (or vise versa) can cause us to chase our tails.  I thought my truck was giving me grief with regard to the charging system as I viewed the voltage,  but it’s been OK.

 

But, the OP may be having a problem.