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ITV emission check 

When it is time for your car’s ITV the most normal items to check would be wheels, tyres, brakes, bodywork damage etc. some of which we have already covered. We often forget about our car’s contaminating commissions. This is one of the fundamental aspects to pass an ITV as it is the most common cause of an ITV failure.

For Diesel engines, the most important test in checking the emission is the opacity of the exhaust gases. The opacity limit depends on when the car was first registered as the laws have changed significantly in the past few years. We are going to clarify doubts you may have.

How are gases measured?

Gases are measures out of the tail or exhaust pipe at the rear of the car. In general, if you follow the manufacturers’ servicing schedules and always use good quality fuel and oil, perhaps you would be less likely to have a problem at this time. This test is performed by putting the engine at idle, then accelerating the car to speed of disconnection. This means to the point where the injection with acceleration is empty. To not damage the engine, the ideal temperature to check this is over 80 degrees centigrade with all external energy drains disconnected as would be lights radio etc.

The reader probe is introduced into the exhaust pipe and is capable of measuring the opacity level or maximum absorption co efficiency which is the smoke that is emitted from the exhaust.

The value of gases for cars registered after 1st July 2008 is 1.5 m-1 but if your car is older then the limit is set at 2.5m-1 for non-turbo vehicles and 3m-1 for those fitted with a turbo. For new vehicles with the new emission sticker ITV Euro 6 and Euro VI this limit is lowered to 0.7m-1. Vehicles registered before 1st January 1980 are exempt.

In the opacity test the maximum number of allowed readings is 8, this allows the exhaust to blow out any residual soot sitting in the exhaust and then get a correct reading. If the result is high then the average of last three readings are used to calculate the final amount.

To test a diesel engine certain steps should be followed:

1. The engine should be hot following manufacturers’ specifications, if there were any,

2. Before beginning the test, the engine would be revved to between 2500 and 3000 rpm for approximately 1 minute so as to reach the desired temperature in the catalytic converter, or DPF.

3. Hybrid vehicles would require the manual override to switch on the engine in order for the test to be completed.