Starting in December 1993, diesel vehicles must be tested for exhaust emissions every 2 years (abbreviated: A.U). This test measures the amount of soot in the exhaust gas. The so-called nephelometry with the help of a combustion tester shows whether the formation of smoke is within the acceptable range. To do this, the engine is accelerated four times to maximum speed - a process in which many car owners break out in a cold sweat. Make sure the engine is warm before doing this check. Thick smoke from the exhaust pipe indicates either poor engine adjustment or significant injector or engine wear.
You can do some preparatory work so that your diesel Renault can pass this test. Conduct an external inspection of the exhaust system, which must be serviceable and tight. A dirty air filter prevents combustion air from entering, so replace the filter if necessary. You also need to check the valve clearance. Having prepared in this way, you can safely undergo an exhaust gas toxicity test either in a car repair shop or at the same time as a technical inspection.