These vehicles use software to control the hybrid system. The software is designed to put the system into a fail-safe mode if there is an internal component failure. This allows the vehicle to travel a limited distance at reduced power.
If the vehicle does not enter a fail-safe driving mode when required, the vehicle will behave as if shifted into neutral, coasting to a stop. While power steering and braking would remain operational, this behaviour of the car could increase the risk of an accident and injury or death of vehicle occupants and other road users.