US Manufacturer (have to) will pass the cost on to consumers.
Foreign manufacturers will respond by placing tariffs on US imports.
US Consumers will reduce new car purchases as prices increase, demand decreases.
Foreign consumers will reduce new car purchases, demand decreases.
US vehicle exports decrease further hurting US manufacturers.
US and Foreign Manufacturers will reduce production to meet.
All resulting in an increase in layoffs in the auto industry worldwide.
You in the auto industry, start saving every penny. You will need it if the tariffs are put in place.