Yes, "all-new" does convey a specific meaning, and the specific meaning is this:
"We want you to buy one and will say anything to try to convince you to do so."
I respectfully disagree with Kosmonaut to the extent that I believe "all-new" doesn't really mean the car is totally redone. It may not even mean it is mostly redone. It may only mean they have put a new name on an old product, with possibly a few cosmetic changes.
Really, advertising-speak is such an ocean of waffle-words that you can't take anything from it to reliably mean anything at all. And I say that as someone who wrote advertising copy before I found a better life. The art of writing such copy is to make the reader think the words mean much more than they do.