Theoretically anything can be a black hole
There are several theories to how black holes form, and the most common way is through the death of a star. There are multiple ways to form black holes, and in theory, scientists believe that you can turn anything into a black hole.
The most important factor is matter and mass. So a car can become a black hole if the right circumstances are in place. If a car can possess 6 kilometers across and still preserve its overall mass, its density could get to an astronomical level causing a strong gravitational force. But of course, this is a theory since there isn’t any known way to shrink an object to that volume while still maintaining its mass.