It will use 3-5x more gas in the winter because of the extreme cold sapping the heat.
Also runs much longer because it's harder to maintain the temp high enough, for long enough.
Many people also would not turn the heater off, which is also drawing heat from the engine, prolonging it further.
And if they don't let it complete to 100%, starts again on next run, etc.
If it triggers and you're already at your destination, best to put it in park, turn off the HVAC and press the pedal down to accelerate the process and let it finish before shutting off the car.
Thanks for the feedback. Last night the midnight outdoor temperature in my neighborhood in Portland, Oregon, when the New Year arrived was 40 degrees F (4 C), which might indicate I haven’t had much experience with ERDTT in the 5.5+ years I’ve been driving my 2012 Volt, nor with experiencing EMM in that level of cold weather.
I take long vacation drives once a year or so, but hover around 99+% ev with local driving, leaving nearly year-length gaps between long trips (endured my third FMM last October). I find it convenient to avoid adding minuscule gas mile numbers to my records by sitting in the driveway until the EMM has concluded. This also provides me with a rare opportunity to "rev" the engine by stepping on the accelerator.
One oddity I do notice is that the energy usage display usually stops increasing the "Gas Used" quantity about midway or so through the EMM, and eventually concludes some minutes later with no more gas being used. This puzzled me until I read a comment in this forum fairly recently that seemed to indicate this could be proper behavior. The smaller motor is first clutched to and then serves as a starter motor for the gas engine. The EMM is intended to make sure the engine is properly lubricated, so, I suppose, once the fluids attain their proper running temperatures, "engine lubrication maintenance" could be handled just as well by having the motor turn the engine’s internal parts instead of burning additional gas to accomplish the same goal... Is this indeed what happens?