What can you do if cosigner will not sign off on car?

Make sure that you have proof of full payment for the loan. Then, discuss the issue with them. Perhaps their refusal is for some other reason? If you owe the co-signer money for the car, you will need to pay it back, but be sure that you keep copies of the cancelled checks/money orders you pay with. Another way to solve the issue is you can ask them to put a lien for that amount on the title, but the title will be in your name. When you sell it, a portion of the sales price will be needed to pay off the lien. However, it is their choice as to whether they will do this if you still owe them money.