The AP2 feature in the Model S currently alerts the user when vision is obstructed and refuses to go into autopilot mode. If you're in autopilot already it make

The AP2 feature in the Model S currently alerts the user when vision is obstructed and refuses to go into autopilot mode. If you're in autopilot already it makes noise and flashes warnings to tell the driver to take over. I assume if the driver doesn't it will slow down and come to a stop, but the one time this happened to me I didn't give it a chance to do so!