somms, thanks for the super useful resistance to temperature chart!
Instead of substituting a fixed resistor I am going to calculate a series or parallel resistor (with a switch) so my 2012 will act more like a 2013 and use ERDTT only below 15 deg. F (or maybe 10). On really cold days I see (feel) the benefit but it is pretty annoying to have it come on at 24 deg. F. So I think lowering the threshold (like the 2013 does) will work better for me, and will also give me a better idea of how cold it actually is outside (with a correction factor).
Chart would be better if it were anywhere close to being accurate!
By the chart,
15Kohms should be @
40F whereas the center console for my 2013 Volt is reading static
58F instead!
Maybe if I get a chance later I may experiment with various other Kohm resistors and report back what other values readback on the display. Keep in mind that the center console temperature display is
NOT realtime as soon as the resistor or even the original sensor is plugged in. You will initially get the max
-40F reading until the BCM consistently reads this value for several minutes. In my case, I installed the resistor at night and of course, the center console initially read
-40F (and engaged the ICE immediately) but by the next morning it had registered at
58F where it has held at ever since. If you have no resistor or sensor attached and power on the Volt, the center console will display
NO temperature value as well as the ICE engaging immediately upon power on.
You could get creative and put 2 10Kohm resistors in series for 20Kohm or 2 32Kohm resistors in parallel for 16Kohm resistance, ect. but I just wanted to keep it simple as possible and the way I have this installed, I am literally about a minute (1ea 9/32 screw away) from reconfiguring the original temp sensor back in if I really had to. The actual sensor will probably get reinstalled eventually in the spring!
Charging System Operation
The purpose of the charging system is to maintain the battery charge and vehicle loads. There are 6 modes of operation and they include:
• Battery Sulphation Mode
• Normal Mode
•
Fuel Economy Mode
• Headlamp Mode
• Voltage Reduction Mode
• Plant Assembly Mode
Fuel Economy Mode
The BCM will enter Fuel Economy Mode when the
ambient air temperature is at least 0°C (
32°F) but less than or equal to 80°C (
176°F), the calculated battery current is greater than -8 A but less than 5 A, and the battery state of charge is greater than or equal to 85%. Its targeted accessory power module set point voltage is the open circuit voltage of the battery and can be between 12.6-13.2 V. The BCM will exit this mode and enter Normal Mode when any of the conditions described above are present.
BTW: Keep in mind that you probably shouldn't pick a fixed resistance that reads back on the center console<
32F since it may possibly throw you out (or in?) of Normal mode for 12V battery charging!?