Why are you required to have a defective exhaust system repaired immediately?

You answered correctly. A defective exhaust system must be repaired immediately because it causes noise pollution, which disturbs others, and loose parts may fall off, creating a hazard for other road users. However, the engine would not overheat due to an exhaust defect, so that is not a reason. In general, a safe and quiet vehicle is required by German traffic regulations to protect both people and the environment. Make sure your vehicle's exhaust system is always in proper working order.