A 2010 crux Chevrolet Cruz 1.6L car with a mileage of about 65 thousand km and equipped with manual transmission. The owner reflected that the engine fault lamp was light and slightly jitter after the car was replaced by the cylinder head and the oil pump in the repair shop for the accident vehicle. Fault analysis: because the vehicle is a breakdown vehicle, the method of combination of seeing, listening, touching and measuring is used initially to detect the vehicle. No obvious leakage, virtual connection and breakage were found when the engine cover was opened. Then starting the engine, it is found that the fault light on the meter is on, and the fuel door is slightly jitter. The failure is exactly as the car owner reflects. Using GDS to check the ECM module, there is a fault code (the position of the crankshaft position is not reasonable). After reading this fault code, the first response is that the timing is not right. Check the timing mark corresponding to the normal position. The electromagnetic valve line of the two camshaft position sensor and the two camshaft position actuator is normal. The two camshaft position sensor, the two convex axle position actuator electromagnetic valve, the two convex axle position actuator, the two convex axle, the ECM module, the engine wire harness have been tried, but the failure is still the same. When the vehicle is tested, it is found that the fault occurs after the hot car starts (), and the engine timing is checked again. Use GDS to read the engine idle speed data for comparison: Figure 1 shows the fault car, the intake camshaft position instruction is 80%; Figure 2 is shown as the normal car, the intake camshaft position instruction is 62%. In order to further analyze and determine the cause of the fault, we decided to use the oscillograph to measure the intake camshaft signal, the exhaust camshaft signal and the crankshaft signal waveform separately. Comparing the waveform with the normal vehicle, it is found that the position of the inlet camshaft is deviated. Then the oscillograph is used to measure the duty cycle signal of the VVT electromagnetic valve of the inlet camshaft of the faulty vehicle and the normal vehicle separately, and the result is the same. Combined with the above waveform, the normal car intake camshaft VVT solenoid valve is pulled out, the normal car intake camshaft position is delayed, and the waveform is the same as the fault car, thus it is correct to determine the gas distribution phase of the fault car. The fault should be caused by the failure of the VVT system. According to the working principle of VVT, the oil pressure is measured. The result is that the malfunction vehicle is 1.5bar and the normal vehicle is 2.1 bar. It is judged that the oil pressure is too small, and the intake camshaft VVT actuator does not reach the position required by ECM, and the fault occurs. Troubleshooting: according to the oil road analysis of Cruz, the oil system includes camshaft lubricating oil path, VVT working oil path, spindle diameter lubricating oil circuit. After checking the size and the bearing of the camshaft normally, the pressure relief part is locked in the VVT working oil circuit. Consider the replacement of the cylinder head in the front repair shop, remove the cylinder head, check the original factory parts, and replace the original cylinder head to solve the problem.