Recently for my Corolla 2003 model showed the engine check sign on. I got the code checked and its say i am required to change the catalytic converter. My factory warranty covers this however the dealer told me to pay 200 dollars extra so that they can also change the Oxygen Sensor. Im not so sure about this. Someone told me that i dont have to. They can still use the old oxygen sensor. Should I listen to the mechanic at the dealer shop? Please advise.