MOT test

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Vehicle meets the requirement for exhaust emission. These vary on the age and fuel type of the vehicle

Test procedure

The MOT inspection covers the vehicles emission levels. The inspector will connect the car to a computer to take readings from it's exhaust gasses. 

The substances that are measured are carbon dioxide, hydrocarbons and carbon monoxide. If any of these levels are excessive then the MOT will be a failure.


Common faults

Emission control system component fault Damaged or work emission control components can cause your vehicle to fail it's MOT test. The emission control system is largely responsible for the "breathing" of the engine. The engine need to control the correct mixture of fuel to air in order to burn the fuel correctly. If the vehicles emissions are high them this may be due to a reduction in air flow. This could be as simple as a blocked air filter, or as complicated as a problem with the vehicles electronic brain.

Engine damage. Engine damage is a very 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 now working effectively then it may cause an increase in dangerous emissions to be released from your vehicle.

Also see: Exhaust system

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