Modifications have been made to the Gen 2 ERDTT settings over the years.
2016, 2017 Volt has for the Engine Assist Heat settings:
Touch On for temperatures below approximately 2 °C (35 °F), or touch Deferred for temperatures below approximately -10 °C (-15 °F).
2018 Volt:
Touch On for temperatures below approximately 0 °C (32 °F), or touch Deferred for temperatures below approximately -10 °C (-15 °F).
2019 Volt:
Touch On for temperatures below approximately 0 °C (32 °F), or touch Deferred for temperatures below approximately -25 °C (-13 °F).
In Deferred mode, when Max Defrost is selected the engine may run at temperatures below approximately -10 °C (15 °F) until the vehicle is powered down.
I also note the following about the 2019 Volts that came to my attention because the driver’s display has been modified from the previous Gen 2 displays, and the owner's manual has had some editing:
It is possible that GM slightly expanded the "usable window" in the 2019 Volt to give it a 57 ev mile range, but did not have it EPA retested, so the rated stats did not change.
I say that because the 2019 Volt owner’s manual has new illustrations for Normal, Sport, Mountain Mode, and Hold Mode in the Driving and Operating section of the manual.
These images reflect the new "analog" type gauge on the 2019 driver’s display where a "ball" marks the actual charge level and the entire gauge is divided into tenths (and, I think, a mark indicating the half way point between tenths). Previous models had ten bars on the battery icon that were green if that tenth of the battery still contained usable power, and not green if that tenth had no more grid power.
The manuals for the 2011/2012 Volts have illustrations for Normal, Sport, and Mountain Mode that show a battery icon with the top two "bars " blacked out, the bottom eight lit up, and 32 miles of estimated range (suggesting that each battery bar represents ~4 kWh of usable power, total range ~40 ev miles).
That illustration remained unedited through the 2013-2015 Gen 1 Volt manuals and also through the 2016-2018 Volt manuals, i.e., top two bars were blacked out to indicate they had been used, 32 ev miles estimated range was showing, and the bottom four bars were grayed out to represent the Mountain Mode reserve. Hold Mode was added, and the battery icon for the Gen 2 Volt was redrawn to reflect the actual Gen 2 driver’s display...
When the Gen 2 came out, no one bothered to edit the illustrations to reflect any increase in usable battery power (even the 2018 Volt illustration continues to show 32 miles of range with 8 bars remaining), or that the Gen 2 Mountain Mode reserved only 2 bars and not 4 bars of power.
Now look at the illustrations in the 2019 Volt manual. They show, in the bottom left corner, an estimated ev range of 57 miles! The illustration for Hold Mode shows the usage ball at the very top, suggesting that the full charge range of the 2019 Volt is, indeed, greater than 53 miles. Also, the illustration for Mountain Mode seems to show the ball indicating the MM-reserved charge is only ~1.25 bars, not the 2 bars the earlier Gen 2 models maintained...
It could be the 2019 Volt does have a "usable window" that is slightly greater than the earlier Gen 2 models. One owner has reported seeing on the energy usage display a 14.5 kWh Used instead of only ~14.0 when the car is driven beyond battery range. What is unknown is if a 2019 Volt owner must then pull more than 16.85 kWh from the wall to get a full charge containing slightly more usable power than earlier Gen 2 Volts to produce a 57 mile range, and if the car’s tested mileage would still remain at the 106 MPGe rating.