[SFLGGRL]

hey guys,
I need some legal advice about selling a car.
I sold a guy my old car, the check engine light was on because the O2 sensor was bad, says the people at Hyundai. I got it fixed but the sensor came on again right before I sold the car. I told the guy about it and he said ok that's fine. I called Hyundai to make sure that they would replace the sensor free of charge because they had just "fixed" it.
Anyways, I sold the car, well, have a down payment on it, just waiting for the rest when I transfer the title, I got the title and it's ready to transfer, but now the guy is backing out because he took it in to have it replaced and they are saying something else is wrong with it now.
Is there anything I can do?