Yes, if the primary borrower on the car loan defaults on the loan, the co-signer may be held liable for the outstanding balance. This is because the co-signer agreed to repay the loan if the primary borrower fails to do so. If the co-signer files for bankruptcy, the debt may be discharged, but the co-signer could still be sued by the lender for the amount owed.
In some cases, the co-signer may be able to negotiate with the lender to reduce the amount owed or to enter into a repayment plan. However, if the co-signer is unable to reach an agreement with the lender, they may be forced to pay the entire amount owed on the car loan.