ICE = Internal Combustion Engine (the regular gas engine). The mode you're referring to is EV (Electric Vehicle). Elliot's description on how to get into this mode is correct... but it takes a lot of practice! I find that you can't just go light on the pedal... you need to go light but quick... a little "stab" to get one bar, then you can slowly add pressure from there to get up to four bars. You can do this from as low as 15 miles per hour up to 60 or more. Best if the road is flat... and important to have plenty of room in front and behind you to practice!

Side note to Elliot... how is it possible that you get almost 58 mpg on your HCHII, but only 40 on the Prius???