The phrase "autonomous mode" refers to a state where a machine, device, or system can operate and make decisions on its own, without needing human control or intervention. Full definition
The vehicle was traveling in autonomous mode at the time of the crash. (theverge.com)
It was in autonomous mode at the time of the collision, with a vehicle operator behind the wheel. (businessinsider.com)
I was surprised by the level of skill with which the car drove itself, but also by how many times it dropped out of autonomous mode unexpectedly. (theverge.com)