He probably just knows you'll pick him up if he doesn't so he holds out, that's how Gator and Libby are lol you can try tossing a treat in the car and seeing if that gets him to jump up, preferably high value like meat or hot dog or something. And/or have someone stand on the other side of the car, door open, and call him and/or hold the treat and see if he'll jump in with one person calling him from the other side. Or have someone sit in the backseat to get him in (they don't have to stay back there). I am sure you have tried all this already though but might help. Could use a toy too if he's not food motivated and/or could start giving him a small treat whenever he gets in/you go for a ride. Speaking of which, try taking him fun places in the car. If you've only ever gone to like the vet or something, he might know that and not want to go in. Could try going to like a pet store, feed store, fast food place, dog park, walking trail, beach, field, something like that if you have anything like that even if it's just a couple times so he learns you don't always go bad places. Or even just drive around briefly and then come back, most dogs just love the ride itself. But I would say wait for him to jump up rather than lift every time cause otherwise they just expect it. Once he jumps in the first time it will be easier. Obviously if you are in a hurry, waiting for him to offer the behavior can be a pain in the neck, but I think it is beneficial. And if you have the time, you can practice jumping in and out of the car at home without actually going anywhere. That way, you have the time to wait for and encourage him rather than being in a hurry and then when you need to be in a hurry, hopefully he will have learned it.
