2011 Curious if it might be some temp sensor somewhere instead of the high power battery degrading?

voltowner said:

Ryan, I have the dongle and MyGreenVolt app ( I do not see the My Volt Control app in the app store is it the same?). Can not find where to see if battery heater is active or working in what I have?

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first screen ("dashboard"?) has four temperature bars: battery coolant, engine coolant, powertrain electronics coolant, and transmission/driveunit. At some point below 32F battery temp, the engine will run continuously to generate power to supply the battery heater. At an even lower point, there will be an alert "Battery too cold, plug in to warm". One indication that the battery heater is working is that the battery temperature will start climbing when you turn the car on. If it starts approaching 50 in less than 20 minutes from 32, that's normal operation.

Normally, the battery heater will keep the battery at or above 32 by drawing wall power. But depending on the model year, it may only do that for three days and at which point it enters a deeper sleep until it's unlocked and started. MGV's dashboard pie chart shows battery heater consumption as yellow. If that wedge is a substantial chunk, that means the heater has been working. that chart seems to be "since the battery finished charging to full" so when the car turns on, you'll see what was used while it was off and any preconditioning you called for, then as you drive, the green propulsion energy segment will start overwhelming battery heat and cabin heat sections.

Okay, this MAY BE relevant sometimes. I did an experiment on Saturday.

Somewhat cool day below freezing, but barely above ERDTT, but hadn't used the car for a couple of days and the battery was cold. I rigged up MGV and the battery temperature read out as 32F. Which is where a plugged in but resting Volt seems to let it drop to. I've never seen it colder until I've not driven for at least three days and the car falls into an even deeper slumber. OnStar stops polling around then too. I'd been niggling about "why are we seeing all these engine running events in winter?" so I wanted to see if I could make one happen. Got the car out, popped on Mountain Mode just as a charm against wrecking the battery, headed for the interstate and punched it.

I got the engine to turn on. No dash message, no ERDTT, no Propulsion Power Reduced, just engine on when there was theoretically plenty of power available. But the battery temperature meter was RED instead of green and it was climbing quickly. 2-3 degrees per minute. Which is a LOT for heating up a 300lb lump. After about 10 minutes the temperature in the battery was up to just above 50F and the meter turned green and the engine turned off and I was back on battery, using charge down to the mountain mode setpoint*.

The point being, though, that the combination of trying to climb up a ramp and barrel down an interstate at 75 with a freezing battery WHILE feeding the battery heater full blast seems like it was just too much for the chemistry to keep up with, and the Volt responded with "Well, I guess I need more power" and kicked on the ICE. The car performed well while doing this, and the engine spun quickly (3200-3500 RPM) though not what I'd associate with "screaming". Most of normal driving may not even use the battery heater and just depend on the intrinsic heat of "battery being used" to warm it slowly up to the point where it starts chilling the battery instead.

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* Mountain Mode for early Volts like mine was documented to be "about 40% battery" in song and legend, but for posterity I watched it cycle between 37% and 39% State of Charge. That's surprising little room between the low and high marks corresponding to engine on and engine off, but it does match pretty well with the 5%-7% range SoC I see on normal CS mode. Which makes me further suspect that all the car is doing is changing where "CS" is for MM, and probably doing the same thing for Hold Mode, and in the latter case, just setting the high "engine off" threshold wherever the SoC was at the time Hold Mode is turned on.