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From a present perspective, environmental protection occupies a position of supreme importance, especially with regard to pollution levels due to motor vehicles. To reduce environmental pollution, the limits for pollutant emissions from cars have been gradually lowered over the past few decades in the type approval procedure and series inspections. The emissions characteristics of vehicles in use are, however, crucial for the pollution level. To check the emission characteristics of vehicles in actual traffic and to monitor observance of the endurance requirements of the exhaust gas regulations, it is absolutely essential to introduce an informative and practical field inspection system on a legal basis. That means that emission measurements have to be carried out in the complete licensing test on the roller-type tester on the basis of the type approval procedure, and this to be done on vehicles with differing mileages from private customers.

The practical qualification of two short test procedures developed for periodic measurements of in use Otto and Diesel vehicles with high emission levels has been proven. From the test results of these vehicles showing outlying emission levels it becomes evident that excessive pollutant concentrations or smoke emissions originate from defective engine components, or incorrect adjustments, respectively, which are relevant to the emission behaviour. Automation of the test procedures contributed to achieve a good reproducibility of the test readings and to keep the measuring time within reasonable limits.