Lots of good advice above, my Dalmation X Bearded collie was a bugger for this as a pup, i tried everything, weeks and weeks of attempts for no advances. In th ened i took her to a remote place with zero traffic and went for a walk. As we approached the car and i got the lead out she started going down on her front legs, wagging her tail . . . .i totally ignored her, got in the car and drove off! Her face was a picture, she paniced and came flying up behind me, i stopped the car opened the door and she couldn't have got in any quicker! Never had a problem since!
I will add that i did this