23 Z battery voltage while driving generally in the 14’s. Last couple 3 days it’s like 12.5. Car starts and run strong, dealer says would throw a CEL if there was an alternator issue etc. Curious if anyone else has had similar experience. Likely heading back to dealer next week, may look at another much farther away.

 

23 Z06 - generally speaking and for the most part, my charging rate while driving with the headlights and A/C off is around 12.5 - 12.8. A couple of times my battery tender tripped off line and the charging rate for a while after starting the car was in the mid to high 13s. It seems to me that with a good battery that is fully charged, the charging voltage you see on the dash is lower compared to having your battery either partially discharged or defective.

 

GM has been using variable output alternators since 2006. If the system doesn't need the juice it will be around 12.5.

 

That's right. From the description I have in the 2020 Service Manual, which applies to Stingray, the charging system will enter the Fuel Economy Mode. In this mode, the generator is not charging - but maintaining the "open circuit voltage" (for an 80% State of Charge). The generator output voltage will be between 12.5-13.1V. Here is the actual description:

'The BCM will enter Fuel Economy Mode when the estimated battery temperature is at least 0°C (32°F) but less than or equal to 80°C
(176°F), the calculated battery current is less than 15A and greater than 8A, and the battery state-of-charge is greater than or equal
to 80%. Its targeted generator output voltage is the open circuit voltage of the battery and can be between 12.5-13.1V. When fuel
economy mode is active, the generator is not charging, only maintaining open circuit battery voltage. The BCM will exit this mode and enter
Charge Mode when any of the conditions described above [conditions for other charge modes] are present."

There are lots of conditions that will trigger other charge modes, such as headlights on, windshield wiper on, or if the HVAC system requests a boost. Unless you have a DTC code, you probably don't have a problem. Not all codes cause the MIL (malfunction indicator lamp) (aka CEL) to illuminate on the DIC. So, you could have your dealer scan for codes just to be sure.

I made a graphic representation showing the minimum and maximum generator output voltages (which is the same as what you will read on the DIC when the engine is running). I tried to summarize the conditions for each. This comes from the manual - I'm not gonna say you will see exactly what it says - because the car can't read. But it shows why a variation in voltages is normal.

 

^^^^
As Andy notes. The alternator voltage is controlled by a computer NO longer the old voltage regulator.

This is what I measured on my 2020 C8.

• If the car sat for say 4 days when I drove to town (25 to 30 miles) the dash reading was ~14.0 to 14.5 volts. It was charging the battery to 80%. BTW that was day time and no wipers operating.
• On the way home there would be a STEP change as the battery reached 80% charge. That was usually to about 13 volts. It's enough to handle the sound system, fans etc BUT not enough to further charge the battery.

Many modern cars are doing that to save energy, GM calls it "Fuel Savings."

 

appreciate all the replies.