New member here. Just joined today. The main reason is because I have exhausted all other resources. And I do mean ALLLLLL other. Including Chevrolet, General Motors, three different Chevy dealers, numerous mechanics, friends, family and the list goes on......I have a 2016 Z06. 29,000 miles, 7 speed. I keep it on the battery tender in a climate controlled garage. Has a brand new Optima Yellow battery. The old battery (Autocraft) was still good but since I had it out I wanted to replace it with the better brand. After it sits a good week or so it is sluggish to start. But all through the day it starts up like a new one. I have my instrument panel set to read the battery voltage constantly because of my issue. Before it starts it reads 2.9 volts. I repeat....2.9. Not 12.9. Not a typo, lol.....2.9. This is why I'm here today. After it starts it goes up to 14.1 give or take a few. During driving, it will stay there most of the time and then sometimes go down to 12.8. Revving, A/C, Radio, horn, windows, etc. do not make it fluctuate. I get back home, pull it in the garage and shut it off. It goes back down to 2.9. Why / How? But it will start right back up like nothing is wrong. Received the same email from OnStar, that I have read on here from a few other Vette owners, that it detects a problem with the starter motor or connection. Service Code SAC004. Please schedule service with your preferred service provider ASAP. I did just that. The Chevy dealer told me there isn't anything wrong and charged me $130.00 for the diagnostic. Also told me that reading 2.9 is normal starting with the year 2016. The $130 charge isn't bothering me. It's the telling me that 2.9 is normal even being connected to the battery tender PLUS starting. 2.9 is not enough to start anything, is it? Since then I have received the same email again this morning. That's why I'm here. Maybe someone out there can tell me what is going on. Sorry for the lonnnnnnng post, lol.

 

It sounds like you may have gotten a new battery that is bad, it does happen regardless of brand, if not, sounds like the starter is going out but wouldn't think so, usually if starter is going out, when you drive it a while and get the engine hot, it will not crank until everything cools back down a while. I would suspect it is a problem with the new battery, may have voltage but the cranking amperage is down.

 

The way I am, I had Advance check both old and new batteries before I bought the Optima. Both had good cranking amps. It was reading the same with the old battery. That's why I'm wondering is there something else faulty? Is there any other C7 Z06 owner out there that's showing 2.9 when it shuts off? I'm trying to upload a pic of my gauges but can't seem to find the right file type.

 

Where are you measuring the 2.9 volts? The car certainly won't start or crank with 2.9v. I doubt the door locks or dash would work either.

What do you read at the battery terminals with a volt meter? Loose or bad connections will cause a voltage drop under any load.

What does the battery read when disconnected? Should be around 12 v even after a few days if the battery is good.

Charging issues can be caused if the SMALL BLACK SENSING WIRE on the negative battery cable clamp is broken or disconnected.

Disconnect the negative battery cable to avoid shocks and shorts, then check the fuses and buss bar on the positive cable / clamp. Make sure all parts have good mechanical connections and fasteners tightened.

Be sure that both battery cable clamps are horizontal, pushed down all the way and then tightened.

After you start the car you are seeing CHARGING voltage. It can be 15+ volts right after engine start and will drop down to around 12.8 v when the battery becomes fully charged.

Let us know what you find out so we can all learn.

GL

Ron

 

Thank you so much for that post. I'm trying to post a pic I took where it shows 2.9v. The battery is good. How I know that is.....the date on it is Sep 21. I had them check both the old battery and this one. The voltage meter read 12 something on both of em.

Here it is. Can someone with a 2016 Z06 post a pic of their volts while not running so I can show the dealer?

 

And here it is running down the the road tryin to loosen my load......Thanks again Ron! You explained why it goes down to 12.8. That makes me feel better.

 

I don't think you have a problem with the 2.9V reading. I also can't find any fault code shown as SAC004.

The voltmeter reads the voltage output of the alternator not the battery voltage level. When you are getting a 2.9V reading the engine isn't running and the alternator isn't producing any voltage. Do you have the car in accessory mode or service mode when you are getting the 2.9V reading?

Here is a link to a C7 Stingray discussion from 9 years ago about the same 2.9 V reading. https://www.stingrayforums.com/threa...-voltage.6239/

Bill

 

Check your ground wires, check that the battery terminals are tight, and also check that the little wire that connects to the negative terminal in the back is also connected and is tight. 2.9v with the car off seems like it isn't measuring the voltage correctly from the battery, such as a loose connection. Then when the car is running it reads the voltage from the ECU with the alternator putting out a charge. Everything else you have mentioned is normal operation.

 

The voltage sensing location may have changed over the model years. I don't see 2.9 on my 2019.

Here are pics from my 2019 GS.. 26 F outside, 36 F in garage



ACCESSORY MODE - DOES NOT DISPLAY PERF DATA



SERVICE MODE - MAINTAINER PLUGGED IN


SERVICE MODE - NO MAINTAINER


SERVICE MODE - NO MAINTAINER - LAST JUNE

I don't recall ever checking my 2014 with the engine off...

Ron

 

Thanks so much guys! Yall have eased my mind a little. I'm not going to worry about the 2.9 reading. What concerns me now is even with the battery tender connected, and green lights on, it is slow to start after sitting in the garage for about a week.. I appreciate all the input. I wish I had joined this forum a long time ago when I had my C4, C5, & C6. This C7 is my favorite of all I have owned. Still getting used to the 650 HP!!!!!!!

 

Double check that the outlet that the battery tender is plugged into shows 110 vac. I had a GFCI fail, but the tender lights looked OK - powered by the car battery until it discharged...

Ron

 

Slow to start or slow to crank? If the started is spinning plenty fast then the delayed start(or prolonged cranking) is normal when the car sits for a week. That is because the high side fuel pressure needs to build back up enough to inject fuel on cold start and sitting for an extended period of time causes the pressure to drop. The high side fuel pump is mechanical and driven off of the camshaft.

2.9v at key on engine off isn't normal and you should still investigate the wiring at the battery to be sure that the battery monitor wires are tight.

 

Center row icon, looks like a box
the nwxt will ask for file type… your library or photos

 

Here is my 2016 Zo6. Def isn’t 2.9. If you want to show your dealer.

 

This is my 2015 Z06 Display:

Accessory Mode Short push on Start Switch without the Clutch pushed in so the car won't start.


Service Mode initiated by pushing Start Switch for about 30 seconds with Clutch Out.


Video showing how Voltage Display changes when going from Service Mode to Retained Accessory Power by pushing the Start Switch once.

There is nothing wrong with the OPS car. My car is one of the last cars built in June 2015 just before 2016 production began. Unless GM did something to change the way the display operates subsequent to when my car was built they will all do this.

Bill

 

On, but not running top pic. Bottom Pic right after starting it. Mine is a 2016 as well. Pics were just taken. I drove this one to work today.

 

What was the voltage level reading right after you pushed the Start Button to turn the engine off? The display will remain on for a few seconds after the engine is shut off. Mine reads 2.9 V.

Bill

 

Hey Bill, sorry I didn't look. I'll try to remember when I drive home tonight and post back.

 

It sure did.

 

Now I'm wondering if it's a difference between an automatic and a 7 speed. Thanks for all the different posts. It will help me when I make OnStar refund me my $130.00. LOL