Why the need for plans?
This is as silly as Google's need for accurate maps to avoid potholes. Any autonomous system must be to a large degree indeed autonomous, as in "able to adapt to prevailing circumstances".
The Audi that drove to Las Vegas had a map (they all need to have an idea where they're going), but for the rest it just had to adjust to other traffic to overtake and manage its speed and lane positioning. What you need in a parking garage is a way to identify what are parking spaces and a way to find the exit again afterwards - in some places I've been that's even hard for a human to work out. The rest is adapting to circumstances: avoid people and objects unless they look like Justin Bieber*, work out where to park and let's hope there is connectivity in the garage so you don't end up having to find the damn thing back amongst hundred of others.
By the way, I couldn't actually care less what gadget triggers it. I already have a smartphone, that's enough for me.
* I can see this giving rise to a whole lot of new "the hacked car did it" crime novels.