When did autopilot become part of the model S? How do you know if the 2013 or 2013 car has it.....is it part of tech package?
2013 cars don't have autopilot. - - - Updated - - - It came late 2014. Autopilot cars have 12 ultrasound sensors. Cars without it have less. I guess 8? I guess easiest way to see the difference is to look whether car has rectangular radar below nose cone or not. http://www.teslamotorsclub.com/attachment.php?attachmentid=59250&d=1410892378
Also, any car manufactured AFTER September 2014 will have the hardware. Now you can activate the software later, but unknown if you could activate the software for cars with the hardware but without the tech package from Oct 2014 - April 2015. As for cars built in September 2014, the above advice is a good way to check. Some may have been produced early in the month without the hardware, but most probably were.