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A BMW 5 series passenger car with a 6HP19 mileage of about 120 thousand km has never been maintained by the 6HP19 transmission. After driving 100000km, there is a phenomenon that the speed of the car is jitter at a speed of 40 to 90km/h, while the engine tachometer is occasionally swinging around 2500r/min, and the speed meter of the engine swings at 1500r/min when the speed is 50-60km/h; the speed of the vehicle is not serious in the above interval when the speed is 70 to 80km/h, when the speed exceeds 100km. /h is basically normal; in addition, when the vehicle is running at a constant speed, there is a clear cough sound on the right side of the gearshift lever, and the sound is most obvious when the speed is 35 to 40km/h. Fault diagnosis: first of all, the related detection, because the fault memory of the electronic control system did not record any fault code, so it decided to pass the road test and combined with the dynamic data of the fault to determine the fault location and the cause of the failure. In the test, it was found that the fault was really like the phenomenon that we used the 5HP19 transmission to repair the Volkswagen Audi car, which was caused by the failure of the twister locking clutch. According to the actual fault phenomenon and the analysis of dynamic data, we think that the fault location is likely to come from the whole control range of the torque converter clutch. For the Volkswagen Audi series 5HP19 transmission torsional locking clutch failure, we will also have the next step to determine the method, and the 6HP19 transmission is completely different from the 5HP19 transmission, it is the electromechanical hydraulic control integrated control, that is, its electronic and hydraulic control unit integrated. We can not make the next judgement through the form of human control, so the cause of the failure can not be determined in one hundred percent ways. Generally in the 5HP19 transmission, this kind of fault can be solved directly by changing the variable twister, but we can't move the 6HP19 transmission. We can only determine the cause and the range of the fault in the decline of the TCC control function, the function of the TCC solenoid valve, the TCC control valve function, the TCC lock of the twister, and the decrease of the electronic and hydraulic control function. The clutch itself and so on. According to the above analysis, we did not lift the transmission from the car, but first started from the electro-hydraulic control unit. In disassembly, we found the poor quality of ATF but did not burn the film, so the valve body was cleaned and the special ATF and filter was replaced. After loading, it is normal to start the test, and then retry after the hot car (especially when a small throttle state is constant) and there is a shrug failure, only a lot less than before. At this point, it is still impossible to determine where the fault is directly, and decide to replace the torque converter according to the experience of maintenance 5HP19. After lifting the transmission from the car, we did not change the twister directly, and decided to cut the twister to see its lock clutch device and make the decision. When we cut the twister, we found that the lock clutch friction plate was intact, and the oil seal and the seal ring were also soft and unhardened, so only the oil seal and the seal ring in the twister were replaced, and the welding of the twister was resumed to reload the car. There was no change in the result after the trial run, and the maintenance was deadlocked. The fault phenomena and fault characteristics are obvious, that is, the control range of the torque converter locking clutch, is it the fault of the electro-hydraulic control unit or the torque converter itself? Is it replacing the new electronic hydraulic control unit or replacing the new torque converter? After all, maintenance has some risks. We can't replace the two major devices. Because of the old twister can not find the problem, and the electric hydraulic control unit operation is relatively simple, we continuously replace two blocks of electric hydraulic control unit assembly, although there are some minor faults in the shift, but the original fault still exists, which basically explains that the cause of the failure is not in the electro-hydraulic control, So we can only change the new twister. After the new torque converter is replaced, a long time trial run is carried out, and the trouble is completely eliminated. It should be that the friction coefficient of the surface of the TCC locking friction plate of the original torque converter can not reach the requirement, which leads to the large fluctuation of the slip speed and the phenomenon of bad friction when the TCC action is adjusted. Although the second case appeared after maintenance, there was a problem before maintenance, but there were more serious problems covering it up. Fault phenomenon: after the overhaul of the transmission, the 3 gears change to 4 gears with abnormal sound. The TCC of the torque converter is locked under the action of small load. Related to model: 6HP full series. The cause of the failure: the coefficient of friction. Solution: replace the upgraded and improved ATF.