Trebor

I bought a new Duralast gold battery last month. I went for a ride this afternoon in my 2006 LS2. I noticed the analog volt meter was around 13 /13.2 while driving. Hmm, that's too low I thought. I switched over to the digital reading and I got the same thing. So when I got home I got my hand held volt meter. With the engine off, the battery read 12.79 v. I thought that is OK. I started the engine and the battery voltage read 14.5 v. So moral of my story, don't trust the onboard volt meter.

919cw313

All of this sounds completely normal to me. There’s nothing wrong with your gauges.

farmington

The alternator puts out 14.5 volts.

Trebor

Engine running:
Onboard volt meter = 13.2v
Handheld volt meter = 14.5v

not normal

dpigguy

Remember that voltage leaves battery at 14.5 but does not go directly to the meter. It will always run less at your dash meter than it does at the battery due to resistance and voltage drop as it finds its way to the dash. Mine shows some 0.5 voltage drop measuring as you did.

FAUEE

Sounds like loose or dirty battery terminals.

919cw313

Ah, I didn’t realized you rechecked the car’s volt meter and the handheld at the same time.

TucoTom

The voltages @ various point was a recent thread on the forum. My vette read the following voltages.
Alternator+ 14.75vdc
Battery=14.62vdc
Fuse Block=
DIC=14.2
I couldn't find the proper place for the + lead in fuse block
What these readings are tell us is the voltage drop @ the various components.

Trebor

Ok, I didn't know that. I thought the onboard voltmeter would be the same as the handheld unit from the battery.

Dano523

Understand what the IPC dial voltage, and the DIC voltage is telling you to begin with.

So quick break down, alternator charges at 14.7 volts. By the time the voltage hits the battery from the alternator, it's down to 14.5. Power from the battery goes to the BCM, then out to the Modules down line in the car.

Now on the IPC voltage gauge, and the DIC voltage reading, it's telling you the voltage at the ECM, since it a digital gauge that is getting the voltage information to post from the ECM. Hence normal voltage on the gauge should be 14,1~14.3 volt with the a/c off, the head lights off, and the radiator ran not running while the motor is idling.

As for car batteries and the motor not running, AGM fully topped off by say a tender, should have a voltage of 13.7, while lead cell battery should be around 14.2 instead.

So your 13.2V IPD voltage (at the ECM , since this is what the gauge dial is telling you) with the car running, it telling me that either the radiator fan and lights where on to cause the voltage drop, or you have a problem between the Engine fuse box to the BCM in the wiring/connectors that is causing the low voltage reading from the dash on your C6.
Note, alternator only puts out about 14 amps at idle, the radiator fan draws about 14 amps, so with it running and say lights on as well, this is the reason that you may end up with less than 14.1volts at the gauge when the battery is going into a draw state/alternator not able to keep up with the amperage draw amount of the system.

So on that note since you are 14.5 at the battery with the motor idling, but in the low 13 at the ecm, would start with first checking the engine fuse box terminal to make sure that the nut is still tight there where it gets is power from the battery.
From there, would pull the upper fuse box to clean the spade connectors between it and the lower boxes.
Next on the list with the battery disconnected, would pull the BCM connectors to give them a good cleaning.
Last on the list, is the ECM connector, and would pull and clean them and double check the BCM and ECM ground connection points as well.

Hence battery at 14.5, it getting full voltage from the alternator to the battery, but down line of the battery from the fuse box, through the BCM ending at the ECM, you have corrosion pin problems isntead. And again, IPC is telling the voltage at the ECM and not the gauge isntead.

Dano523

The fuse block is checked at the center post that the battery cable is connected, and you want to use the top of the post, since a loose terminal nut will cause a drop.

But at 14.2 at the IPC gauge (the ecm at the end of line through the BCM that the gauge is reading), tells you that everything before it, is fine. Hence its when the gauge voltage is less than say 14.1, that we have to play the find the problem game from the alternator, to the battery, to the fuse block, to the BCM, and then to the ECM instead. As for final check, helps to have a Tech II, so you can check the voltage at the BCM, as well as the rest of the other modules down line of the BCM. Hence ECM is on one path down line of the BCM, and although it an easy one to solve, ECM may have good voltage, but RCDLR on it voltage lines may be corroded and it has low voltage isntead.

dpigguy

What he said ^^^^^ I gave you the cliffs notes version. Dano523 is the expert!