Mileage of about 81 thousand km, equipped with BJH engine, matching 01M automatic transmission in 2008 FAW Volkswagen Bora GP1. 6L car. User response: when the vehicle is running, there is no indication of speedometer. If the parking brake is not released during the driving process, the meter will not alarm by buzzing. Fault diagnosis: first, connect the fault diagnosis instrument V. A. S5051 to detect the vehicle, read the control unit fault memory, and do not have any fault codes. The fault diagnosis instrument is used to perform the self diagnosis of the components. The functions of the meter are normal, indicating that the execution function of the meter is free from malfunction. According to the control principle of the vehicle related system, the author determines that the vehicle does not release the parking brake in the course of the vehicle. The reason that the instrument does not call the alarm is that the instrument does not receive the speed signal, and can not judge the vehicle in the running state, so there is no alarm. Generally, the reasons for vehicle gauges not working include speed sensor damage, circuit fault and instrument damage. The speed signal comes from the speed sensor G22, and the speedometer indicates the control path is the differential driving wheel. Speed sensor G22. Instrument signal processing. Pointer indication. In this case, the speed sensor should be checked first. Because the car is equipped with a 01M automatic transmission, the sensor that signals the speed meter is a G22 speed sensor located in the differential position. For this purpose, we measure the power supply of the G22 first. According to the related circuit diagram, the sensor plug No. 1 foot is powered by the sensor, and the power supply is normal (fuse S710A). The signal line of No. 2 foot is connected to the meter T32/28 foot, and its conductance is measured by the multimeter; the 3 foot is the sensor of the sensor, the iron lap is in the middle of the flow trough, and the iron lap is normal. After that, the waveform of the sensor G22 was observed by using the oscilloscope function of the fault diagnosis instrument V. A. S5051. First, enter the DSO function of the measuring instrument mode. It is necessary to connect the red line pen with the sensor 2 feet, and the black pen is connected to the battery negative pole. After starting the engine, put the transmission lever on the D position and let the wheels rotate automatically. Normally, the oscilloscope will appear regular square wave signal with the speed of the wheel, but the vehicle does not detect any output signal. Therefore, I initially decided that the sensor was damaged, and Yu Shixian replaced the speed sensor. After replacing the sensor G22, the signal output waveform of the sensor is measured again, and it is found that there is no signal output. Is it a problem with the new sensor? So the vehicle speed sensor was removed by hand, and the deflection of the instrument pointer was found. The sensor worked normally. The trouble spot can be identified as the damage of the sensor drive wheel on the flange shaft of the differential. After disassembling the transmission, it is found that the driving gear of the speed sensor on the differential side falls off. Troubleshooting after maintenance. The Bora car has a special speed sensor on the transmission to provide speed signals for the instrument, and golf and Jetta are also the same structure. The structure of the automatic transmission and the manual transmission is that the sensor signal is transmitted directly to the meter. In addition, the 01M type automatic transmission also has 2 transmission speed sensors G38 and G68, which are located at the top of the transmission. The function of G38 is to record the rotation speed of the sun gear in the planetary gear system and transmit the signal to the automatic transmission control unit J217. The function of G68 is to record the output gear speed and transmit the signal to the automatic transmission control unit J217. In the process of maintenance, the maintenance personnel must pay attention and do not confuse. In addition, the speed signal of the speed and the sedan car is provided by the ABS forward wheel speed sensor, and the signal is received by the ABS control unit J104. Then the signal is transmitted to the other control unit through the CAN bus. The control unit connected on the power bus can get the signal from the CAN bus as long as it is required.