I searched for this problem and couldn’t find anything relating to this.

Does anyone know why when I rev my 2000 C5 that the voltage in the DIC goes from 14.3 volts down to 12.7 then goes back up? I think I might have a problem lurking but not sure. I put a red top in about a year ago and really haven’t had any issues other than me leaving the lights on and making it go dead one night. When I am driving around town at night with the wife the other night I noticed when the lights were on and I would run the windows up the head lights would go dim just a little but didn’t cause any problems.

I am no expert that’s why I’m asking all of you. I can handle a Battery issue but if it’s the Alternator I know those are not cheap!

Any advise?

Thanks guys.
David

 

If the voltage goes down as the revs go up, a belt may be slipping. The momentary dimming lights when you roll a window up or down is normal.

 

Dave

The C5 charging system is very sensitine to changes in loads. It is normal to see flickering due to brake lights, cooling fans, etc.

Check and clean chassis grounds G-101, 102, and 104. There is a large ground terminal on the passengers side of the block. Just follow the negative battery wire down and you will see where it connects. That connection needs to be clean and tight.

Insure that both battery terminals are clean and tight. They need to be tightened to 11 foot pounds. Then check the 12 VDC + connection on the BACK of the alternator and the connection on the starter solenoid.

BC

 

Thanks guys, I will check all of that when I get the chance.

 

Very important.

 

What your seeing is a normal situation, the voltage regulator is doing it's job of regulating voltage and 12.7 volts is the lower end of it's range.

 

Guys....I too have this same issue and it is driving me nuts! I saw the volts on the DIC ranging back and forth...then one NIGHT, crossing the Nevada desert I watched the volts drop 13...12.7....12.3......12.1.....12....11 .8......11.5......11.2....11.....10.9... .10.8......and one by one the computer shut down the unneccessary electronics.....then when my fuel pressure went from 60 to 50 and then 40 the car shut down. I replaced the alternator thinking that the issue. BTW..has a new Yellow Top Optima. The GM dealer bought replacement ($425.00 by the way) worked for about a month then did same thing on same desert trip (what is going on in the Nevada desert at night???). I finally took both alternators to Pep Boys and they ran a check showing both functioning normally. Put one back in car. Battery at FULL charge. Turned on car and got same "CHARGE SYSTEM FAULT" and no useful codes other than telling me voltage low...duh. Checked battery with my tester and showed full charge. Checked ALTERNATOR with car running and NO OUTPUT measured. NOW..GO FIGURE. I am stumped. And my car is grounded. Now I am driving my 96 Discovery and it is hurtin' me bad..
I have a 2001 Vert with an A and A Vortech supercharger. I ask this....could belt slippage completely stop any voltage from alternator? As I recall, the voltage reg is integral to the C5 alternator? SOMEBODY help me because I don't buy the slipping belt, bad battery (used two new Yellow Tops). Worse is the computer has decided NOT to be helpful either. Damn gremlins!!!!!

 

Ron

I seriously doubt you have belt slippage! If it were me in your shoes, I would take the car to a certified starter alternator repair shop and have them do a complete test on the whole charging system. Most of the time they have better equipment and people who know how to use it. They will tell you whats wrong with it.

BC

 

I drove mine around last night and watched the voltage. When the engine was running it never dipped below 14.2 except for very momentarily when I held the power window switch or turned on the headlights. (and that was for only a split second). Revving the engine only made the voltage fluctuate in the tenths of a volt. Again, the slight headlight dimming when you hold the window switch is normal, but if the voltage drops into the 12 volt range when you rev, you definitely have an issue with the alternator, regulator, or belt. (think about the grounds, too. It takes a good ground for a good current flow in any circuit)