The exhaust system is an essential component of your motor vehicle. Firstly, the exhaust helps to direct noxious gases away from the cabin, so you will not be exposed to gases that can harm your immediate and long term health.

Another important function of the exhaust is to make sure your car is being as fuel efficient as possible, by monitoring the levels of oxygen emitted and using this information to balance the fuel/air mix of the engine to the optimum level.

Your vehicle is likely to fail an MOT test if it isn't working as effectively or efficiently as possible, here are a number of common MOT failures in relation to your exhaust:


The car will be connected to a special type of computer to measure carbon dioxide, hydrocarbons and carbon monoxide levels to check they are not excessive, if they are found to be high the vehicle will fail the MOT.

This can be caused by a faulty emission contol system component, such as a blocked air filter or the vehicles eletronic component that controls the mixture of air and fuel, so that the fuel may burn correctlty.

Engine damage can also cause poor exhaust emissions, such as a cylinder rings or damaged pistons can lead to bad exhaust emissions.

Another common fault leading to poor emissions can be caused by the catalystic converter, catalyst or cat. Any car produced on or after 1993 was required to have a catalyic converter fitted, they were fitted to reduce the amount of dangerous gases exiting the exhaust, it does so by breaking the gases down to less dangerous substances.

Physical exhaust system 

The exhaust must be complete and secured to the vehicle it must silence effectively and have no serious leaks.

It must be silenced efficiently depending on the make and model of the vehicle. It may fail an MOT if it is too loud.

Loose mounting of the exhaust can result in an MOT failure.

Exccesive corrosion on the exhaust sytem can result in exhaust leaks and in most cases will be an MOT failure.

Missing baffles in the silencer can lead to excessive noise levels

© Best Motors. All rights reserved.