MOTs – exhaust emissions testing requirements

Every domestic vehicle over 3 year’s old, is required by law to pass an MOT that has been carried out at a Government-certified testing station. The purpose of this test is not to ensure that your vehicle meets the minimum standards that the law dictates on the day of the test, but also to ensure the safety of other road users and the environment. An essential part of the MOT test is now vehicle exhaust gas emissions testing. This is carried out to ensure that the exhaust gases emitted by any vehicle are within the permitted levels stipulated by both national and European laws.

During the MOT each vehicle has to meet the minimum standards for exhaust emission, though this varies depending on the age and the type of fuel the vehicle uses. In further articles we’ll have a closer look at these differing criteria.  The examiner connects the vehicle to a computer during the MOT and takes readings and measurements from the exhaust gases that are emitted. If any of these levels are exceeded, then the vehicle will fail its MOT and will need to be re-tested after the necessary repairs have been undertaken.

The common reasons for exhaust emission MOT testing failure

A damaged emission control system component fault

Damaged or faulty exhaust emission control components are one of the major reasons why vehicles fail an MOT. The emission control system is largely responsible for the ‘breathing’ of the engine. In other words, for any car to function efficiently and cleanly, the engine needs to control the correct mixture of fuel to air. If the vehicle emissions are high, then this is usually due to a reduction in the flow of air. This may be due to a simple problem like a blocked air filter, or may indicate a more complicated fault with the vehicle’s engine management system.

Engine damage

Engine damage is a common cause of poor exhaust emissions. For example a blown cylinder head gasket can lead to excessive oil consumption. This in turn will lead to an increase in level of hydro carbons in the exhaust emissions. The same result will be experienced with various other engine component failures such as cylinder rings or damaged pistons.

Catalytic Converter

All modern cars are required to be fitted with a catalytic converter, sometimes referred to a catalyst or cat. The job of the catalytic converter is to break down exhaust gasses to less dangerous substances. If the catalytic converter is not working effectively, then it may cause an increase in dangerous emissions to be released from your vehicle.

If you’d like more information on vehicle emissions and MOT testing, why not call Bakestone Motors on 0161 483 7526. Bakestone Motors MOT specialists in Stockport.