A catalytic converter, as the basic engine combustion processes occur before exhaust reaches it. However, removing or driving without one is illegal, triggers a permanent "Check Engine" light, and can cause the engine computer to run the fuel mixture improperly, hurting fuel economy and long-term performance.While the car will still run, doing so without a functioning converter causes several immediate issues:Increased Noise: The converter acts as a partial muffler. Removing it will make your vehicle significantly louder.