If you have not paid the full down payment, the lender may consider the vehicle to be in default and may be able to repossess it. However, the specific laws and regulations regarding repossession vary from state to state, and it is important to consult with an attorney or review your loan agreement for specific information about your rights and responsibilities.
In some cases, the lender may allow you to make up the missed payment or work out a payment plan to avoid repossession. It may be possible to negotiate with the lender to return the vehicle voluntarily in exchange for settling the outstanding balance, but the terms of such an agreement would depend on the specific circumstances and the policies of the lender.