The mileage is over 225 thousand km, and the 2003 volkswagen golf cars equipped with 01M automatic transmission. The cold car is normal, the hot car is delayed, and when the engine speed rises to 2800r/min, it barely rises to 2. When it rises to 3600r/min, it can go up to the 3 gear. Fault diagnosis: this car has been sent to the service station after the failure, and is diagnosed as the internal fault of the transmission because of no fault display and no abnormal sensor. But the owner was not convinced of this diagnosis, so he went to my office for examination. After receiving the car, the author verified the fault phenomenon, which completely coincides with the owner's statement. The results are the normal oil pressure, the transmission oil no odor, the oil quality clear and pure without impurity, the oil level conforms to the standard, and the automatic transmission control unit has no fault code. But when using V. A. G1552 to view the dynamic data flow of the automatic transmission, it is found that the oil temperature of the transmission is rising too fast, and the phenomenon of delayed lifting of the gear rise after the car is combined with the car. The author analyzes the following. Will the oil temperature sensor signal shift and give the control unit a false impression? Then we measured the oil temperature sensor, and in the specific temperature range, the measured value coincided with the value provided by the maintenance manual, indicating that the hypothesis was not established. The temperature of the transmission radiator is monitored with an infrared thermometer. After a period of time, the temperature of the transmission oil rises abrupt to 120cC, and the fault appears again. This indicates that the fault is caused by the high temperature. If the fault is caused by the high temperature of the transmission, what is the cause of the high temperature of the transmission? The possible reasons include clutch, brake skidding, poor lubrication in the box, locking of the torque converter locking clutch, and poor heat dissipation of the radiator. There was no abnormal running speed and abnormal speed during the lifting and lowering of the vehicle. The slip of clutch brake could be eliminated. If the body is not lubricated in the body, it will cause the wear of the planetary gear mechanism and the bearing copper sleeve, which will cause the sun wheel to be bald, but the car does not find these symptoms, so it can also exclude the bad lubrication. If the torque converter locking clutch can not be locked, it will cause the oil temperature to rise. After testing, the TCC locking work is normal, and the torque converter has been locked for a long time after a very long time, and the oil temperature remains at about 120 degrees C, and the torque converter should be excluded from working. If the radiator does not heat properly, it will directly lead to the high temperature of the transmission. To further confirm that the temperature of the inlet and outlet of the transmission radiator is measured by the infrared thermometer, it is found that the temperature difference between the inlet and outlet is very small, so the heat dissipation of the radiator is suspected. Unload the radiator, dredge with a wind gun, blow out a lot of yellow sediments, and use the cleaning agent to clean up after repeated cleaning. After a 2h test, the temperature of the transmission oil is kept at about 96~97. The lifting gear is restored to normal and the fault is ruled out. After asking, the owner of the car added a different brand of antifreeze in more than one year, causing the cooling system to be corroded and produced a large amount of ion particles, causing the radiator to clog. Fault summary: when the radiator is blocked, the flow rate of coolant in unit time is reduced and heat dissipation is bad. The transmission oil that flows back to the oil bottom carries a lot of heat, which causes the oil temperature to rise rapidly. The control unit can perceive the current oil temperature anomaly through the voltage signal obtained on the oil temperature sensor, so as to achieve protection. The purpose of the transmission is to implement a protection and control mode for the time lag. The automatic transmission protection function is a working mode of the automatic transmission control unit. What time, what conditions to meet and what protection is performed depends on the software version of the transmission control computer. The author's understanding of the thermal protection function shown in this case is as follows. (1) the automatic transmission with the oil temperature sensor is mainly to monitor the two state of the low temperature and high temperature of the transmission, because in the low temperature, because the poor fluidity of the transmission oil will affect the lubrication, the timing of the gear lifting is delayed and the transmission is in the low load state as far as possible. The purpose of transmission and engine. When the oil temperature of the transmission reaches the set high temperature limit, the transmission also has to carry out the control of the delay lifting timing, because if it is upscale, the torque converter increases the oil temperature of the transmission because of the increase of the load torque, so it also plays a role in boosting the oil temperature, which will cause the transmission to run. Slippage and poor sealing and malfunction, delay the timing of the shift so as to reduce the heat generation. Based on the above two points, when the transmission oil temperature is low, the opportunity to delay the upper gear can play a warming effect, so as to protect the transmission and engine and reduce wear. When the transmission oil temperature is high, the time to delay the upper gear can restrain the oil temperature rise of the transmission and achieve the purpose of protecting the transmission.