Maintaining MOT Emissions Standards
To enable continued compliance with environmental requirements, VOSA conduct exhaust emission checks in two ways. Firstly, VOSA Examiners carry out metered emission checks at the roadside and secondly certain classes of vehicles that are subject to an MOT Test will receive at least one metered or visual (dependant on date of first use) check per year.
Roadside Emission Checks
How is the check carried out?
The test is carried out by inserting a probe into the exhaust pipe and measuring the emissions. The reading given by the test will indicate whether the levels comply with the MOT test standards. If the emissions levels do not comply with the requirements the driver of the car will be given a prohibition notice stopping use of the vehicle.
What do I do if I get a prohibition?
For a minor offence, the prohibition will generally be delayed to give owners a short period to have the vehicle repaired and brought back within legal limits. If your vehicle is greatly exceeding the limits you will not be allowed to carry on your journey until the defect has been put right.
In either case you will have to carry out the necessary repair work and have the prohibition cleared within 14 days or you will be liable to prosecution. You may be cautioned at the roadside. The prohibition notice will explain what you must do to have it cleared. You will normally be required to have a full MOT test.
To enable continued compliance with environmental requirements, VOSA conduct exhaust emission checks in two ways. Firstly, VOSA Examiners carry out metered emission checks at the roadside and secondly certain classes of vehicles that are subject to an MOT Test will receive at least one metered or visual (dependant on date of first use) check per year.
Emission Checks within the MOT
Petrol And Gas Powered Vehicles
Vehicles to be tested
In-use exhaust emissions testing is applied to all petrol and gas-powered vehicles with four or more wheels.
The test does not apply to vehicles fitted with 2-stroke engines.
The emissions test to which a vehicle is subject will depend upon its date of first use (i.e. date of registration) as follows:
- vehicles first used before 1 August 1975 a visual test will be applied.
- vehicles first used on or after 1 August 1975 a metered test will be applied.
On 1 January 1996 a new test was introduced for petrol fuelled passenger cars fitted with advanced emissions control systems such as three way catalytic converters. The test was extended to include large petrol fuelled passenger cars and petrol fuelled light goods vehicles from 1 August 1997.
It is important for owners of vehicles fitted with catalytic converters to understand that the catalyst is only one in a number of components, which collectively make up the emissions control system. Experience has shown that there are a number of reasons why vehicles fail the emissions test and in many cases defects, which lead to excessively high emissions, are often rectified by a simple adjustment. These defects can usually be rectified at little cost to the owner.
Where replacement parts are necessary, costs can increase significantly. For day-to-day use of the vehicle, and care of the emissions control system, owners are advised to consult the vehicle handbook or seek advice from the manufacturer’s agent/dealer.
Accurate diagnosis of engine management systems often requires the use of diagnostic equipment and appropriately trained vehicle technicians. Motorists should, therefore, seek advice from reputable vehicle repairers before agreeing to repairs.
Diesel Engined Vehicles
Vehicles to be tested
This inspection applies to all diesel engined vehicles with four or more wheels.
The smoke test to which a vehicle is subject will depend upon its date of first use (i.e. date of registration) as follows:
Visual smoke test
For all private cars and light goods vehicles up to and including 3500kg design gross weight first used before 1 August 1979, a visual test will be carried out.
Metered smoke test
For all private cars and light goods vehicles up to 3500kg design gross weight first used on or after 1 August 1979, and for all heavy goods vehicles and large passenger vehicles, a metered smoke test will be carried out.
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Page last updated: 03/05/2006