Have the 5.3L Flex fuel LS California 2WD model with 113000 miles. No problems until Aug 2012, (original battery died). Now volt gauge pegged maximum, then minimum, now swings between +18 to +11 or 12, sticks when vehicle off, or no battery connected. Bad gauge in cluster I now suspect. Or maybe the stars are aligned just right... Here are the details.

Day one volt gauge swings to well over +19 volts after 1 mile of driving. Turn around and put into garage. Dropped the negative cable on battery and gauge drops to below 9 as normal for no battery connected. Checked battery and read 12.5 volts. Connected negative cable, started vehicle. Needle raises to normal +15.5 or so position. Drove vehicle 6 miles, city driving speeds. 4 miles into test drive volt gauge pegs maximum again. Headed back to garage and needle slowly lowers to +9 volts, off the low side of scale, just as I am parking in garage. No notice of any other system, accessories failing, dimming, rough idle, etc.
Replace alt with remanufactured made by "Remanny". (160 amp Bosch regulator like the original). Test drive shows things as normal, 15.5 volts on roadway at city speeds. Day two... All normal for a 3 mile trip. Shut off while at work. 9 hours later, within 5 minutes of starting, volt gauge pops up to 18.5 volts, one red line tick mark. Settles back to 15.5 volts within 3 miles later.
Days three and four. Normal on startup. Swings from +17 to +12. All city driving. Sometimes needle pegs at a +16 or so and sticks there. Even when vehicle is shut off. Disconnect negitive on battery and it stays at +16. Start vehicle and and it frees to swing. Then shut off vehicle and it returns to the normal off position.
Load tested battery, reads "good" but low charge. Thinking the reman alt had a faulty regulator, I replaced the remanufactured alternator with another remanufactured alternator by "Delco". Same issues occurring. Anyone else have this issue before or am I the Lone Ranger here? Thanks for the suggestions in advance.

 

I believe it is the vehicle control module that has taken the place of a good ole working voltage regulator. If the voltage is doing as you say, thats what I'd look at. If you have a voltmeter, and this does this at idle, piggy back the meter into the connector, you should see the field voltage all over.

 

Chevy had a problem with the stepper motors that operate the gauges. There was a recall on some vehicles. This might be your problem and if it is the other gauges will soon follow and also be erratic. If it is at 19 volts at idle, put a voltmeter on the battery and see what it actually is. If the voltmeter shows 14 volts or so, the system is good and the stepper motor is bad. If the meter also show 19 volts, fix it quick before your battery is ruined.

 

You need to check directly at the battery with a meter to see if dash matches the meter. If your meter matches the gauge you have a problem. If the meter reads normal the problem is the gauge on the dash

 

KevinKPK; I couldn't find anything about a "Vehicle control Module". Did you mean Electrical CM? If no, can you educate me?
OldChevy & MDTahoe; In my searches related to this problem, I did see lots of electronic gauge issues with Chev dash clusters. That is what lead me to my guess of a bad gauge. I haven't tested volts at the battery or the alt when running. When the volt meter reached +19V going into a 12V battery, I didn't want to get to close to that battery. I didn't think of matching the "at gauge" reading to the "at battery" reading. I'm embarassed I didn't do that before my initial post. I will post more after proper testing. Thank you all.

 

I followed the comments from OldChevy and MDTahoe. Thank you! Tested battery with meter when gauge was reading oddly, (too high or too low). Gauge showed 18.5 volts and meter connected at battery and also at the alternator showed 15 volts. The gauge is now stick again at the 14Volt mark with the engine not running. I will order new stepper motors and install. If this issue reoccurs I will continue the post. Otherwise, thanks to all whom read and replied to me.