Under what circumstance does a technical defect in the exhaust system prohibit vehicle operation?

1. When the exhaust system produces noise levels or toxic pollutant emissions (CO/hydrocarbons/smoke) exceeding established national standards, or lacks a muffler.
2. When the exhaust pipe is painted in silver paint.
3. When the exhaust tailpipe has minor exterior dust.
4. When the catalytic converter is newer than the car body.