I had the unpleasant experience last Friday morning of walking up to my Volt and finding it totally dead. You could only open the front door with the mechanical key. The 240V charger was connected all night, but that didn't help. When 12V was applied to the booster terminals under the hood, the car could be started immediately. I saw that the main battery had been fully recharged during the night. As the owners manual promised, the main battery then started charging the 12V battery. The dealer had to completely recharge the 12V battery later that morning.

As most Volt owners know, dropping the 12V supply causes the main battery to immediately isolate itself. That's what the 12V "cut me" wire in the left side of the trunk is all about.

Chevy suggested that I left the car on all night. That would mean that I ignored the warning bongs and I didn't notice the lit headlights when I plugged in the charging cable. I don't think so.

I asked my dealer, my Volt adviser, and OnStar if they could check the microcomputer logs to see if the Volt had actually been shut off at 10PM Thursday. None of them could do this.

The CPU's obviously keep logs, but the knowledge of which CPU and how to access the log is kept in GM engineering. I understand GM can remotely access a Volt through the dealer diagnostic tool, but only engineering would know exactly how.

I am concerned that if there is a fault in the battery or low voltage electrical system, I could lose engine power, power steering, and power brakes while going 80mph down Texas I10. This would not be good.

Can anyone get me in touch with GM Engineering? My 2011 Volt is 3047 and the Volt adviser has the details.

Thanks

PS: No problems since Friday

PPS: Love my Volt!

Leaving the car on all night won't do this, and if the APM is working correctly, there's no risk of it dying on the side of the road. While you need 12V battery power to start the car, once it is started the APM (the DC-DC converter in the trunk floor) carries the 12V bus using power from the traction battery. (And so if it'd been on all night the car would have been running the APM and the 12V battery wouldn't discharge in the first place.)

The couple of dead 12V batteries we've had in the past have seemed to center on Bluetooth issues. Do you have a phone paired? Were you using it shortly before turning the car off?

I think there was a couple instances of battery failure as well.

It's really no big deal to have a 12 volt display device on a power port device just to see the voltage. Check it every now and then.

PLUS if you hold the start button down ( 15 secs ?) the car goes into a accessory mode.

Does this mode time out ?

The dash display is different but I have never left the car in this mode for over 5 mins.

Does anyone know if the 12V battery is a cranking or deep discharge? I suspect a cranking battery isnt needed. I think if mine goes, I am going to go with an Optima deep discharge battery in its place.

Does anyone know if the 12V battery is a cranking or deep discharge? I suspect a cranking battery isnt needed. I think if mine goes, I am going to go with an Optima deep discharge battery in its place.

It's an AGM battery - and any replacement needs to be as well, because it's under the cargo floor in the passenger compartment.

I think there was a couple instances of battery failure as well.Keep in mind, just becuase batteries were replaced, doesnt necessarily mean they had failed. It is very common for an automotive battery to be replaced under warranty (after a complaint of run-down) in pursuit of customer satisfaction. (much to the chagrin of warranty reps I might add) ;)
WOT

if the APM is working correctly, there's no risk of it dying on the side of the road. While you need 12V battery power to start the car, once it is started the APM (the DC-DC converter in the trunk floor) carries the 12V bus using power from the traction battery.

Dying on the side of the road is OK. Losing power steering and braking at 80mph is a big deal.

It was my impression that disconnecting the 12V battery causes the main battery to isolate itself immediately and unconditionally. Cutting the "cut-me" wire in the trunk is an example. Am I wrong?

There was no cell phone voice traffic Thursday night, but my iPhone is paired with the car and I might have used data features. Is that enough Bluetooth activity to drain the 12V battery? I don't think iPhone data functions involve the vehicle at all.

Dying on the side of the road is OK. Losing power steering and braking at 80mph is a big deal.

It was my impression that disconnecting the 12V battery causes the main battery to isolate itself immediately and unconditionally. Cutting the "cut-me" wire in the trunk is an example. Am I wrong?

Yes, you are wrong. You are making incorrect assumptions as to what happens when the 12V battery goes dead or is disconnected ONCE THE CAR IS ON.
Once the car is ON, technically you can even remove BOTH the + and - terminals from the 12V battery and essentially nothing would happen, (well other than some DTCs indicating a 12V charging issue is present) But your 12V systems, HV battery managment, braking & steering assist etc etc would remain fully functional. This is because once the car is ON these are being supplied 12V directly from the DC-DC converter. So the 1st Responder "cut cable" you referred to in your initial post, isnt really just a battery cable, it also includes a 12V "wake up" feed to DC-DC converter so it SHUTS DOWN when this cable is cut by first responders in the event of an accident.

But of course you apparent "dead 12V battery" condition isnt really related to any of this. One thing we HAVE seen is people leaving their cars ON accidentally. Would that have been possible here???

WOT

But of course you apparent "dead 12V battery" condition isnt really related to any of this. One thing we HAVE seen is people leaving their cars ON accidentally. Would that have been possible here???
WOT

OK, that deals completely with the safety issue. Thanks for the info.

Would leaving my Volt on with the 240V charger connected and working (the main battery was at 100% charge as soon as the Volt was finally turned on) actually drain the 12V battery in 12 hours? Perhaps the 240V charger cuts power once the main battery is fully charged and the 12V battery then starts to drain.

Second question: It used to be that a complete discharge sapped the life of a 12V battery. Is that still true? I'd love to test the "car left on with charger connected" scenario on Saturday night but not if I will degrade my 12V battery. Now that I know that a 12V jump instantly enables the Volt, I can do this test myself.

Thanks again WOT, you should write the book!

I had the identical experience as mikeg3. I think I might have left power on overnight. Once jumped, she started right up and the traction battery was fully charged. Dealer found nothing amiss, did nothing and no problem for the last 8 months.

The same thing happened to me yesterday - car in garage overnight, had 23 miles left on charge when I checked it the previous day, came out to start the car to go to work and found it completely dead. No lights, nothing. After 2 jumps to get it fully going - the first jump resulted in every idiot light and warning to turn on the dashboard, the 2nd jump was more successful and turned the engine on as well. One remaining 'engine malfunction' light was left on (icon of an engine) and I took it to the dealer to have the codes checked and cleared. All working fine now after the cleared error codes.

We think that we left it on after pulling it in the garage - ignoring the chimes and lights that were left on. Marital bliss can be saved by a louder notification - it was my husband who pulled it in the garage after we were washing the car. Seems that GM needs more than a soft interior chime (that you can't hear from the outside of the car with the windows up and doors closed) when you walk away from the car with it left on.

My issue was amost a year ago. I think we need to be careful to turn the ignition off. I think the combination of electric quiet and keyless will do us in.