It's important to keep an eye on the performance of your exhaust components because every MOT test requires an emission test to be carried out on your car. If there are holes in your exhaust system then the emission test will reveal an unacceptable and therefore illegal percentage of toxic emissions, and your car will fail its MOT test. But keeping an eye (and an ear) on the health of your exhaust system is important for another vital reason: if the exhaust isn't taking by-products such as carbon monoxide from spent fuel away from the car, they may be misdirected inside towards passengers instead. If your exhaust is not working properly, your car will be noisy, unpleasant to travel in and suffer from poor performance.