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Failure phenomenon: a 2003 car Guangzhou Honda accord 2.3 L car (using automatic transmission), because the speed meter and odometer on the dashboard are not indicated by a repair plant, but the purchase of a new instrument assembly is in the post test, and the speed meter and odometer are still not shown. Fault diagnosis: first, the road test, the speedometer pointer and the odometer liquid crystal counting system do not work, but the engine running normally, automatic transmission jump gear is also normal. Remove the instrument chief, find the speed signal input terminal (blue / white line) without pulling down the wire side connector, drive with the analog signal generator (Boan 8901 meter), the speed meter pointer display the speed, and the mileage counter also works. It will also be normal to test the instrument that is replaced. It is preliminarily judged that the assembly of the instrument should be no fault. The fault should occur on the speed sensor or the speed signal line. According to the information, the speed sensor should be three terminal Holzer type, but the sensor was not found in the engine room. Because the vehicle is equipped with a multiplex transmission system, it is not known whether the speed signal comes from ABS or automatic transmission system. Remove the multiplex control device located in the driver's side dashboard and check the abnormal condition. It is found that the line that is consistent with the speed signal line is input to the terminal B14 of the multiplex transmission control device. Under the helplessness, reload the side connector of the traverse, put up the fault detector, raise the sedan military lifter and read the data flow. At this time, we find a noticeable phenomenon that can read the speed signal in the data flow, and when the D gear is hung up, the speed signal number can rise with the opening of the throttle. High, which means that the speed signal has entered the electronic control unit of the engine, so there is no need to find the so-called speed sensor. But why the speedometer and odometer do not show that they are trying to enter the automatic transmission system and the ABS system, they can also read the speed signal.