The mileage is about 189 thousand km, the BMW 5 Series car equipped with N52 engine and 6HP-19Z transmission. The customer is unable to increase the speed, and the vehicle is stuffy. Fault diagnosis: according to the customer description, to test the car, in the test process, there is no problem, the place of rapid acceleration, also did not find abnormal, nor alarm phenomenon, before the customer reflected a transmission temperature too high fault, the car has been inspected at the service station many times did not find problems, finally Clean the water tank, but the problem is still. Repeatedly testing the car, it is found that the speed of the engine is rising when the speed of the car runs to 60km/h again, and the transmission will not change the gear, and then the speed of the vehicle will be accelerated by the speed of F. According to the previous maintenance experience, it is determined that this is caused by forced fall. However, there is no phenomenon of increasing speed and stuffy customers. According to the customer description and the problem reflected by the test car, the problems that can cause the problem will be divided:. Engine power shortage. Transmission slippery can not normal shift. Exhaust is not smooth causing engine power loss. Sensor damage inspection does not correct engine data information according to the above analysis to view one by one, Connect ISID to diagnose, do not find any fault, read the relevant data stream also did not find any problems. In the electrical components can not be found, only further inspection from the mechanical components, check the back pressure of the exhaust system, from the measured value of the three element catalyst has not been blocked, the stall test, the original refueling, the tachometer can be 1500r/min, it seems that engine power has no problem. In order to further check the problem, and consider that the car has more mileage, not changing the transmission oil, and after further communication with the customer, the transmission is disintegrated, and the interiors have not been found. Only the bearing of the input shaft has large clearance, but it should not affect the normal driving of the vehicle. In order to guarantee the maintenance quality of the vehicle, the bearing with the input shaft was repaired. After the assembly of the vehicle, the vehicle was tested together with the customer. No exception was found. The vehicle was handed in and the problem was solved. But after two weeks, the customer came in again to reflect the problem and was more serious than before. Again after the test, it was found that the vehicle was not the same as the original. It was obvious that the speed of the tachometer had been rising and the speed of the car had not changed obviously in the acceleration to 60km/h. In the stall test, it is found that the engine speed is not up to 1000r/min, indicating that the engine power is insufficient and the fault code of only one DME detonation sensor 1 is detected by the diagnostic instrument. The fault code is re read after the fault code is deleted and the fault is again disappeared again. Again, the stall experiment is done again, the power is also available. So, when the test comes back to the shop, the problem appears again, reading the fault code, or the above fault, which is very strange, the power has, and a short time. I'm going to analyze the fault. If it's a knock sensor, then the fault should always be there. If the pressure of the cylinder is not enough, it will not be sometimes, sometimes not, it should be not, it will not be the pressure of the cylinder. If it is the leakage of gas, it may occur. If it is caused by this problem, then the camshaft or valve or valve oil seal can be considered. The cylinder head is taken down and disintegrated to find, the camshaft is seriously worn, the valve seal face is also a lot of leper. This situation does cause the engine power shortage, the damaged things are replaced after the replacement of the car test, the problem is still the same, the fault code is the same, this time the engine is no problem, transmission does not There is a problem, or in fact, the important information is ignored in the diagnosis. In order to stop the curve and try to find the law of the problem repeatedly, it is found that every time when the problem appears, it will report the fault of the detonation sensor 1. We know that the detonation sensor is used to measure the engine jitter. If the detonation sensor continues to send out the information, the engine control module will constantly correct the ignition timing. The injection volume is indirectly controlled to prevent detonation. Look at the circuit diagram, as shown in Figure 1. The detonation sensor connects the engine control module directly. If the control module is damaged, it is the same result. In order to determine whether the control module is damaged or the detonation sensor is damaged, the P of the No. 1 and No. 2 detonation sensor is interlocked. If the detonation sensor 1 is still reported to be damaged, the control module is damaged, if reported. The failure of the detonation sensor 2 can be judged to be the damage of the sensor. The result is that both number 1 and 2 are reported to fail. Then there is another result, the sensor has no problem, and the problem should be on the control module or the line between the sensor and the control module. First check the line problem, it is found that the No. 1 pin and 41 pin of No. 1 sensor are broken between the pins and the wire harness box of the bundle is opened. It is found that the wire harness near the left side of the car body is broken, and after the repair is repaired, the problem is completely disappearing. Every time you encounter a problem, you should look for the rule, so that you will not take a detour.