A hybrid electric vehicle has a feature that could allow the engine to start and run without warning. What is this feature called?

The feature that allows a hybrid electric vehicle's engine to start and run unexpectedly is referred to as idle stop. This system is designed to enhance fuel efficiency by shutting off the engine when the vehicle is idling, such as at traffic lights or in stop-and-go traffic. When the driver is ready to move again, the system can restart the engine quickly and seamlessly without requiring manual intervention. This practical design allows for smooth transitions and helps reduce emissions during those idle periods. The idle stop feature is particularly beneficial in hybrid vehicles, which aim to optimize energy usage and minimize fuel consumption.

In this context, the other options do not accurately describe this functionality. Silent start typically refers to the vehicle’s ability to operate quietly upon starting, often found in electric or hybrid cars to reduce noise levels. Auto restart might suggest a feature that automatically starts the vehicle, but it doesn’t specifically capture the mechanism of restarting after idling. Engine revival is not a standard term used in the automotive industry for this specific functionality related to hybrid vehicles.