Nice describe with some details from a GM Techlink article: http://www.sandyblogs.com/techlink/J...chlink%20F.pdf
Volt Engine Operation in Cold Ambient Temperatures
[UPDATE]Volt owners may notice that during a cabin conditioning (remote start) event in cold ambient temperatures, the internal combustion engine (ICE) runs even with the vehicle plugged into a charger. Owners may also note that while driving in cold ambient temperature the ICE will run for extended periods or cycle on and off. A message will display on the instrument cluster that states ENGINE RUNNING DUE TO TEMPERATURE. This may occur even when the battery is fully charged. No DTCs will be associated with this condition.
At ambient temperatures of approximately 25° F (–4° C) or below, the ICE will operate to assist in warming the coolant used to warm the vehicle’s cabin. After the coolant temperature reaches approximately 150° F (65° C), the ICE will turn off and remain off (as long as the battery state of charge is sufficient) until the engine coolant temperature drops to approximately 104° F (40° C), at which time the ICE will restart. This function will continue as long as the ambient temperature is approximately 25° F (–4° C) or less while driving. After the ambient temperature rises above approximately 25° F (–4° C), the vehicle will resume normal electric operation (as long as the battery state of charge is sufficient).
This is normal operation and no repairs should be made to correct this condition.
You typically can limit your Engine Running Due to Low Temp ERDTLT by using COMFORT and low fan settings (1,2,3).
Late 2012s have a Very Cold config option that changes the temp from 25F to 14F. Hardware change.
Update: Response from ari_c's Volt Advisor
[/UPDATE]The difference for this feature is actually in the hardware itself, because the heating system is designed differently. Unfortunately there is not an upgrade for the engine assisted heating options, but if this changes in the future we'd be happy to let you know.