When I start my car the voltage reads 11.5 to 12 volts. After running for a few minutes comes up to 14.0 volts. Just Replace the alternator in June 2018.
I hope it not the alternator this soon. Also Battery was replace in Nov. 2018.
It a 2008 C6 Corvette.

 

Just reading somewhere: "When running you are measuring the output of the alternator, which should be 13.5+, so you are good there. With engine off you are measuring battery voltage, which should be at least 12-12.5, so 11.5-12.5 is a pretty uncertain range. It should also seriously consider a second battery with perko switch (11.5 is dangerously close to not starting an engine). If it was 11.5 when you first shutdown then you would replace the battery." Hopefully it help you.

 

Sounds to me like the battery is on its way out.

 

That battery is dying... if you car is going up into the 14v range it is charging.... so your battery is discharging quickly either from parasitic drain, or just losing it lifespan.

 

Isn't a fully charged battery supposed to be at least 12.6 volts?

 

If you have and know how to use a multi meter I would perform a voltage drop check on the positive and negative sides of the charging circuit...to read positive side connect red lead of volt meter to battery positive and black lead to the B+ side of the alternator...shouldn't be more than .5 volts but I like to see less than .3 volts...to check negative side connect black lead of voltmeter to battery negative and red lead to the alternator case...find a clean spot and usually .2 or less volts is OK !!!...good luck !!

 

Keep a tender on it at night. That should extend the battery life

Clif

 

When i first purchased my 08 I was in Washington DC and I noticed the charge had gone down to 12 volts. It normally charged at 14.2 volts. I was able to get into a dealer and after checking the system I was advised the charge rate was handled by the ECM and after a while it returned to normal. Occasionally I note the charge to vary slightly, but mostly remains in the 14.2 range.

 

That is correct.

 

And of course this should be done with some load on the system, like headlights and A/C blower motor on.

 

Your scenario says weak battery. To initially show a low charge voltage is the alternator trying to put it's full effort into catching the battery charge up to where it belongs. Once there the charge voltage will go to 14 or so volts.. Full potential is available but not needed at that point. It's called "New Battery".

 

Quick reference points,

Put the battery on a tender over night and check the voltage when you pull the tender off. The battery should be 13.2'ish if a AGM, and should be 13.7 if a standard lead cell.

Start the car, turn off the lights/radio/AC, and the voltage with the motor idling should be 14.7V DC with the case of the alternator as the ground, and the terminal under the rubber boot on the back of the alternator as the positive source.

Now go to the battery with the engine still idling and check the terminal with the muliti meter set to DC 20 volt, and should have 14.5 volts on the battery at the termials.
Pop the engine fuse box cover, and using it terminal at the positive source, start with the battery negative terminal as the negative source first, then next the alternator body as the negitive source, should still have 14.5 volts.

If good at the alternator, but low at the battery and engine fuse block, you have a problem with the positive cable that goes from the alternator to the starter solenoid terminal (corrosion or the nut is loose). If you get 14.5 using the alternator as the ground, but lower voltage using the battery terminal, then cable from the battery to the engine block just above the starter has a problem (again either corrosion, or loose bolt).




That out of the way/have 14.5 volts at the engine fuse block terminal, time to check the rest of the system from the engine fuse block to the modules themselves in the car.
The low down is the power goes from the engine fuse block, to the BCM, then out to the modules. I bring this up, since the gauges on the dash are not telling the power at the dash, but the power voltage at the ECM instead. So here is where a Tech II comes in handy, since if you have low voltage at the ECM (which it's power is coming from the BCM), then you could have lower voltage on other modules in the car as well. So with a Tech II, able to read each modules voltage to determine where in the cars connectors/ground point the problem lies. If across the board, then we know that the BCM connectors and its ground point will need to be pulled and cleaned to solve the problem. If just at say the ECM, the its it connector from say off the BCM to it, and it ground point that will need to be cleaned/resolved.

So to sum it up, post your voltages at the give check areas with the DIC voltage, and should be able to come up with a quick fix to the problem.

 

^^^ excellent info, thanks