An exhaust system is a combination of boxes and pipes that direct emissions towards to rear of the vehicle.
All exhausts produce six gases, three of which are toxic; nitrogen oxide, carbon monoxide and nitrogen monoxide. A faulty exhaust can lead to the fumes being drawn into the vehicle and prolonged exposure to exhaust fumes can make a vehicle occupant feel drowsy so it is important to ensure yours is working correctly.
The police can warrant the removal of any vehicle from the roadways on the suspicion that it is producing excessive amounts of pollutant gases from the exhaust. Your vehicle will fail an MOT test if the exhaust system has a fault resulting in incorrect emissions levels being recorded.
Ideally you should have your exhaust checked once or twice a year dependent on mileage to look for corrosion, cracks, leaking joints, broken hangers, worn rubber mountings, failed gaskets and high levels of pollutant gasses.