Jackob

Hey all, I've read a few threads on this and am a bit up in the air after reading regarding what the issue actually is, so I'm starting this thread to get your thoughts.

Car is 2006 C6Z. The voltage varies considerably while driving - while cruising/rpm's above idle it will be in normal range and then at idle it will hunt all over the place, but generally trending low, and dipping in to the 12's so as to every once in a while cause the DIC to prompt: "Service Charging System."

I changed the battery as a step one (it was old) and at the same time had the alternator tested at Autozone (actually took it out and handed it to them to test). It passed their tests...

So, with the new battery and the original alternator bolted back up, it's still acting as I described above (albeit with the voltage generally being higher, but still dipping into 12's sometimes).

Can we confidently conclude it's the alternator that's out, e.g. the regulator?

Thoughts? Thanks!

Unreal

One other option is the tensioner or belt is slipping. I would put a fresh belt/tensioner on and see if that helps. Cheap to do anyways.

Odds are the alternator is probably bad. Mine use to be ~12.5-13.0 then I went to one of the billet tech ones and now it is a rock steady 14.3V.

timd38

The Billet Tech may cost more, but like most things in life, you get what you pay for. I bought mine for all the wrong reasons (good looks), but now that I have it the voltage is, as Unreal stated, at a rock steady 14.3V.

VET4LES

With my Optima Digital 1200 on all weekend I run 14.4 volts all week. Best investment I've made for the C6. The price was right also.

timd38

Hope you got a deal on that charger! It is the best I have ever used.

VET4LES

I got the best deal possible and I'm grateful for that.

Jackob

Bah, bit the bullet and picked up a factory AC Delco. Thx guys.

ant21b

Voltage should be at least 0.5 volt above battery voltage with car running at all times and this is with everything on lights,heater,windshield wipers,radio etc.

shawnaj7731

OP I had the same issue, but after trouble shooting I have a 25% ud pulley balancer, and realize i needed an overdrive pulley for the alternator as it caused my issues to bounce from 12 to 13.8 volts causing the service charging system light at times also. Tsp has them for cheap.

timd38

Who is TSP?

Unreal

Texas Speed

shawnaj7731

https://www.texas-speed.com/p-146-as...or-pulley.aspx
texas speed

Jackob

Factory pulleys on my car. I wonder the tune on the car to accommodate the cams has the idle set too low for the factory alternator? Is there a minimum ideal charging rpm that anyone knows of?

shawnaj7731

850 i think

shawnaj7731

That was the information i got form mr alternator or something www

Jackob

Well here's a rather frustrating update. Having concluded that the problem must be the factory alternator since the voltage was still dipping drastically when not cruising, I replaced it with another factory alternator. It's still doing the exact same thing!

So I now have 1) a brand new battery; 2) a brand new alternator; and 3) voltage that keeps dipping into the 12's at idle (and the DIC says "Service Charging System."

I'm now at a loss. Any thoughts?

timd38

Is the belt slipping?

Jackob

Thanks for the input! Checked the belt and it looks good (the ribs) and it has good tension. No belt dust that I see either. Bah!

cclive

The alternator voltage is controlled by the BCM, not an internal regulator. Since the output of an alternator drops off rapidly as its' speed goes down, my bet is that it is spinning a bit too slowly at idle. A slightly smaller pulley would help, but as long as it charges OK when you are actually driving, I wouldn't get too worried about it.