A Volkswagen Santana 2000 era Superman car with a mileage of over 200 thousand km. The car was repaired by accident, and the phenomenon of acceleration and fuel consumption increased after repair. After receiving the car: read the trouble code with the V.A.G1551 fault diagnosis instrument, and find that there is no stored trouble code in engine ECU. Consider carefully. According to the accelerated failure phenomenon, it is known that the fault should be related to the intake system and ignition system. Check the intake system did not find any blockage. Starting the engine, reading the data flow and observing the control of the ignition advance angle, it is found that the ignition advance angle of the idle speed is small, that is to say, the ignition is too late, and the value of the engine is not obviously increased as the engine speed rises. According to this, the failure of the detonation sensor can be judged preliminarily. To measure the 1,2 cylinder detonation sensor, pull down the wire side connector of the detonation sensor and measure the wire resistance between the upper terminal 1,2 and the engine ECU terminal 68,67, 0.3 ohm normal parameters, indicating that the sensor line is good; the resistance of the 3 connector terminals on the measuring sensors is infinitely large, indicating the terminal technology. Kuang Zhengchang; the resistance between the 3 terminals of the measuring sensor and its outer shell is infinite, indicating that the 3 terminals are insulated from the housing. The same method detects the 3,4 cylinder knock sensor, which also shows normal. So the change method test is taken, but when the 1,2 cylinder detonation sensor is dismantled, the tightening torque of the bolt is small, and the 3,4 cylinder detonation sensor can be screwed down, and the tightening torque is also small. Troubleshooting: the 2 detonation sensor bolts are re tightened according to the technical requirements before commissioning, and the failure phenomena disappear. Read the data stream again, and the ignition advance angle value is displayed in the normal range. Fault analysis: the piezoelectric detonation sensor used in the Santana 2000 age Superman car is strictly required for the tightening torque of the fixed bolt, otherwise the error signal will be transmitted to the engine ECU to cause the engine to ignite. The car has been repaired after the accident, and the maintenance worker does not tighten the fixed bolt according to the technical requirements when loading the detonation sensor, which leads to the insufficient pre pressure of the inertia weight in the sensor. The inertia weight increases with the vibration of the engine, and the force exerted on the piezoelectric element is too large, leading to the EC of the piezoelectric element to the engine. U output a higher voltage, so that ECU mistaken that the engine was detonate and delayed the ignition time.