If you turn the car in, the lender will sell the car. If they sell the car for less than what you owe on the loan, you will owe the difference and they can send you to collections if you don't pay it.
If they sell the car for more than you owe, they have to send you a check for the difference and you do not owe anything else.
It is much better for you to turn the car in if you can't make the payments instead of letting it be repossessed. If you let the car be repossessed, they will add the cost of repossessing the car to what you owe, and then you will owe even more.
