321.436  Mufflers, prevention of noise.
  Every motor vehicle shall at all times be equipped with a muffler in good working order and in constant operation to prevent excessive or unusual noise and annoying smoke, and no person shall use a muffler cutout, bypass or similar device upon a motor vehicle on a highway.
[S13, §1571-m18; C24, 27, 31, 35, §5061 – 5063; C39, §5034.45; C46, 50, 54, 58, 62, 66, 71, 73, 75, 77, 79, 81, §321.436]

For applicable scheduled fine, see §805.8A, subsection 3