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A Mercedes S600 car with a mileage of about 60 thousand km, a M137 engine and an automatic transmission, and a chassis model of W220. The malfunction of the vehicle is: engine idle speed jitter is obvious, acceleration is weak, engine fault light has been lit. After taking the car: the connection diagnosis instrument is self diagnosed, the engine system has multiple fault codes, of which one fault code is P203 D (the right column camshaft is incorrectly phase), and the other is related to the ignition loss. Clear the fault code and check the cylinder running smoothness data. It is found that the data of the 6 cylinders in the right-hand column are larger. It is suspected that the ECI ignition module (N92/1) of the right-hand cylinder is not performing well, replacing it with failure. The self fault diagnosis is repeated, and the fault code P203 D can not be completely removed. According to the working principle of the M137 type engine, the phase angle deviation between the right cylinder cam shaft and the crankshaft is 15. Above, the engine control module will set the fault code. The valve chamber cover of the left column cylinder and the valve chamber cover of the right column cylinder are opened to check the air distribution phase. It is found that the right column camshaft timing sprocket is lagging the angle of one tooth. Re proofread the valve timing mechanism. After completing the test run, the engine returned to normal and the overhaul work was finished. When the camshaft timing sprocket deviates from the angle of one tooth, the air matching angle will be more than 15 degrees, and the engine control module recognizes the fault to activate the engine fault lamp. Incorrect valve timing causes poor cylinder operation, so the engine control module stores ignition missing fault codes. The reason for this failure is not using the correct method to assemble the engine. At present, the new Mercedes Benz engine adopts the timing chain and the timing chain installation method has the following rules. For example, M112 and M137 engines have 2 camshaft timing sprockets, 1 crankshaft timing sprockets and 1 timing chains. In the assembly process, it is noted that the L mark of the left column camshaft timing sprocket is marked with a mark between two copper chains of the timing chain, and the R mark of the right time cylinder camshaft's timing sprocket is aligned with the other two chains of copper chains in the timing chain.