A vehicle with a mileage of about 150 thousand km, a chassis model of W463, a 642 type V6 diesel engine, and a 2009 Mercedes Benz GL350 sports multi function vehicle with a CDI4 common rail injection system. User reflection: the car engine lights out. After receiving the vehicle: the maintenance personnel detected the engine control unit, and found that the fault code 2065---- left air flowmeter B2/6 and the right air flow meter B2/7 were faulty. In road test, air flow data were observed at medium load condition, and it was found that it was nearly 10% lower than the calculated value. After removing the air flow meter, it is found that there is oil stain in the sensor part. At the same time, it was found that there was also oil stain on the air filter. Clear the trouble code, clean the air flow meter, replace the air filter after road test. The engine fault light is lit again in the trial run, and the fault code is the same as before. Using the same method to observe the data of air flow meter, it is found that this time is rather high. Carefully check the parameter setting of the engine control unit, it is found that there are 2 parameters of air filter air permeability compensation value and air flow meter pollution compensation value in the air flow column. After the engine control unit's data is refreshed and tested, the fault phenomenon vanishes. Then the source of the oil pollution should be completely eliminated. Inspection found that turbocharger oil leakage, which is the source of oil pollution. Troubleshooting: replace turbocharger, troubleshooting thoroughly.