【Fault description】
    According to the driver said this car from Guangdong when the purchase of less than 30,000 km. The car on the highway when driving suddenly can not speed, speed up to 80km / h. The road test found that the car when the file has a clear sense of impact, and the automatic transmission does not shift, the engine power shortage, the engine speed to 6000r / min, the speed was only 85km / h.
    【Inspection process】
    First check the line, check the assembly when there is no bad connection. In the automatic transmission control line through the place, one by one check each line, found in the transmission main plug at the root of a light yellow line break. The road is connected after the road test, the fault is still as mentioned earlier. As the car is not equipped with automatic transmission dipstick, to the oil level and oil quality inspection to bring a lot of inconvenience. According to the driver said this car has been added automatic transmission oil twice, has caused automatic transmission oil added too much, resulting in transmission fluid spill. It is decided to decompose the automatic transmission assembly. Automatic transmission assembly after the decomposition of the inspection, did not find any wear and burning phenomenon. So the relevant parts of the thorough cleaning after the installation test, but the fault remains the same.
    【Fault Analysis】
    This car for the assembly car, automatic transmission for the whole electronic control, driving and locked in the second gear position, hanging gear impact, such as automatic transmission hydraulic control failure, it is determined that the car for the circuit failure, resulting in automatic variable speed into the security mode The Mercedes-Benz original electronic testing equipment on the car automatic transmission system fault code read, read the fault code has more than 6, so that it is impossible to have so many parts of the failure, may be false code. With a special instrument to its fault code cleared, the road test all normal, the fault disappears. And thus concluded that the line failure caused the computer to enable security mode. But the car to the user, driving a few days after the failure of the phenomenon again. Again with the original dedicated decoder for fault code read, the fault code for the automatic transmission within the two speed sensor failure. Repeatedly check the automatic transmission of the wires, connectors, lines are normal, and the sensor should not be damaged at the same time. According to the car circuit check also did not find the problem, once again cleared the fault code after the road test, the vehicle and normal driving. Since then the car often appear the above fault, but also find the fault point where, but clear the fault code, the vehicle will return to normal, people puzzling.
    【Maintenance】
    Finally, access to the relevant maintenance information that the Mercedes-Benz car-controlled automatic transmission with automatic transmission oil for the special automatic transmission oil, can not use other automatic transmission oil instead, once the use of other (non-dedicated) automatic transmission oil, the car automatically The transmission will automatically enter the safety protection mode for security protection. At this point the computer will record some trouble code. Finally, the car for a dedicated automatic transmission oil after the failure to completely remove the fault.
   【Maintenance】
    In fact, like this new style of high-end car repair, the key is to repair information and special testing equipment, blind maintenance will only cause more trouble.