The ICE (engine) will fire up after about 5sec to warm the fluids and the cabin. One can stop this by pressing the EV mode button with the 5 seconds. Be aware though that the cabin will not be warmed without the ICE running. EV mode will self cancel if throttle is depressed too far or the charge level drops low. Unless one is just repositioning the car in a parking space it's probably best to let the engine start and provide warm and demisting the windows.