There is no way to "protect" yourself as a co-borrower: if the loan is not paid, the lender may 1) seek payment, in whole or  in part, from you; 2) take collections and/or legal action (e.g. a lawsuit) against you; 3) report your default (if you do not pay) to the credit rating agencies.That is not to say that you may not be able to, in in turn, sue the borrower for amounts he/she owes, either under the original loan agreement or under some subsequent agreement with you (e.g. an agreement whereby he/she keeps the vehicle and makes all payments)--you do have legal rights against the other borrower. However, you cannot absolve yourself of your obligations/liability to the lender, unless both the lender and the other borrower agreed to allow you off the loan.