Carlos Hernandez

Thank you in advance for reading this,
I have a 2010 C6 base with 140k miles, 6 speed manual.

The Voltage gauge reads 15.2-17.0 Volts all the time. It will start on a cold start at 16.5-17.0 volts and work its way down to 15.2-15.8 volts.
Let me begin with what I have tested:
I have replaced the alternator and have tested the new and old one 6 times (I work at a parts place, very easy access for me)
The battery is a brand new AutoZone AGM battery.
If I put a Multimeter to the battery as the car is running it is extremely consistent at 13.2-14.3 volts.
Load testing the alternator on the car yields the same voltage results as the multimeter.
Using Tech2Win I have verified that the ECU is receiving 13.2-14.3 volts (identical to multimeter reading).

The only thing I can think of is that the gauge is just simply wrong, I have exhausted my brain with picking at this. The car drives perfect, just that gauge reads high.

Thank you again,

Carlos

Dano523

Start the car and let it idle, make sure that the A/C and lights are off, then with a multi-meter set to 20v DC, use the body of the alternator as your ground point for the meter probe, and on the back of the alternator under the rear back rubber cap, use that as your positive source for the meter.

Voltage should be 14.7V DC with the engine idling and if higher, then either the alternator voltage regulator is bad, or you have major problems with the ECM that should be controlling the voltage regualtor of the alternator at 14.7 volts.

As for the voltage dial and the DIC, its not telling the voltage at the dash, but the voltage at the ECM (with is powered by the BCM, and which the BCM is powered by the engine fuse box..

A write up I did on fixing alternators, but if your case, this simple write is is not going to help if the alternator is putting out more than 14.7 volts since it has a bad voltage regulator to start with.
https://www.corvetteforum.com/forums...nator-fix.html

Carlos Hernandez

Thank you for the reply!
I have already probed the engine bay with a multimeter to verify that the voltage is not too high. I understand that both the gauge and DIC in the car read ecm voltage, however through 3 different scanners ( torque pro, Innova lat3100, and gm techII) I've verified the ECU is seeing 12.5v-12.8v engine off. And 14.2v-14.7v with the engine running.

Aside from the voltage when the car is running, the voltage also reads about 1 volt higher when the vehicle is off. Which leads me to believe that the gauge is just wrong.

Thanks again,
Carlos

Dano523

Motor idling, AC, radio, lights off, I need the following voltages

At the alternator alone.
At the battery terminals alone,
From the engine fuse box terminal as the positive source, alternator as the ground source.
DIC voltage.

The numbers should be,
14.7 volts
14.5 volts
14.5 Volts
14.3~14.1 Volts (again, voltage at the ECM and the power to it coming from the BCM fuses, and then back at the engine fuse box.

And to point out, the reason that you get the above voltage drops as you move away from the alternator, is the nature of the beast with DC as it goes through the long runs of wiring.

If tell me which is the lower than normal voltage, I can tell you where to check for the problems.

As for motor off, DIC may read a slightly higher voltage, since there is less draw from the other systems at this point.
Hell the reason that we want the A/C off for the voltage test, is when you turn it on, it turns the radiator fan on which has about a 16 amps draw when the radiator fan is running/shews all the above voltage numbers since the OEM alternator only puts out about 14amp when the motor is at idle/puts the battery into a drain state to drop the above voltages.

As for DIC reading above actual battery voltage, then there is a problem in the system isntead. The quick way to track this problem down, use a tech II to pull all the module voltages, and it will point you to a problem with either a connector, or ground wire problem for that module/back at the BCM that is sending power to that module via it fuses.