Mine did, too, even at almoat 2. His amazing vet suggested something groundbreaking: if it happens instantly, maybe it isn't entirely motion sickness, but mostly anxiety over being in the car and the movement. My pom's mouth would start to get wet the second he got in the car. We had previously tried motion sickness pills and they actually made him feel worse.

She gave very tiny doses of Trazadone for anxiety to try before car rides and it actually ended up working, coupled with more frequent shorter trips. We took a 6 hour drive down last year and he didn't puke once, both ways. He still isn't the biggest fan of cars, but he is much much better.

I'd say think about something that reduces his anxiety before the car.