Defaulting on a car loan, which is by very definition a secured loan, will result in the vehicle being repossessed. If you realize you cannot make your agreed payment, start by proactively contacting the lender and trying to work out a reduced payment rate.
Although car loans aren't typically made through the banks for used vehicles, you may wish to consider a used car to keep depreciation and purchase price lower. Different car manufacturers offer financing for used cars and personal loans for lower priced vehicles may also be an option.