Exactly. The absolute limit for EV mode is somewhere between 40 and 45 miles per hour. Like the Prius this limit is determined by the redline of the motor/generator. Once you get to that speed (42 MPH in Prius) you must spin the ICE to protect the motor/generator from overspeeds. Under the right circumstances (downgrade) you could spin the ICE without fuel or spark, but there'd have to be enough downgrade force to keep you from slowing down as the engine would impart some braking force in that situation.