Fault phenomenon:
The Millennium Sea Lion Car that configures the 4y engine travels at 60 to 70km / h, and the speedometer pointer often has a beating.
Troubleshooting:
According to the information of the owner, the speedometer is normal when the speed is below 60km / h, and after more than 60km / h, there is an amount of beating at the same time. 10 consecutive trucks, there is three times, and 3 beating amplitudes are different. First, the fault code is read with the Golden K81 decoder, and the result is no fault code display.
The extraction of the sea lion 4Y engine car speed table signal is completed by 1 Hall sensor, the sensor is inserted on the output shaft of the transmission, and the Hall element is driven by the slope gear, output the square wave signal, and the speedometer is converted to the corresponding Magnetic field strength, push the pointer to rotate 1 angle, thereby displaying the speed value. From the problem of fault nature, this is a non-regular gap failure. For such a fault, it must pay attention to the timing when measurement, and only the data detected in the fault phenomenon occurs. The vehicle speed sensor has three wirings, one line is a 8V sensor power supply, and a line is a sensor iron line, and the third line is 4.5V sensor signal line. The speedometer controller is calculated by pulses on the signal line.
According to the analysis, this beating may be generated at a certain interference signal, and the strongest interference signal on the car is the ignition system. It is to be confirmed that it is not the interference generated by the ignition system. You can only ask the Jinde K80 oscilloscope. "Take the mirror" Tour. Such as ignition system interference, the waveform should be shown in Figure 1, but actually measure the waveform in the event of a fault, as shown in FIG. 3, the waveform at the time of failure is shown in FIG. 3, and Fig. 4.
Waveform analysis:
If the 5V signal line of the speedometer sensor, the signal waveform should be down from 5V, and the mutation portion will be at a right angle.
If it is a sensor power cord, a ground wire, a signal line intermittent break, the sensor signal waveform should return to 5V position, and the mutant waveform should be at right angles or burrs.
If the precision of the triode in the sensor is not high or poor performance, the signal waveform will be filled in the signal waveform, which is caused by the characteristics of the triode. At this time, the triode is working in the saturation zone.
The Hall speed sensor used in the car, the waveform of the fault is measured, two rounded angles appeared in FIG. 4, indicating that this additional rounded signal is generated by the triode of the Hall speed sensor, also That is to say, the fault waveform is caused by poor performance sensor.
Be
Troubleshooting after replacing the speed sensor.
Maintenance experience:
In practice, the maintenance person is the most commonly used method of faulty vehicle, first use the decoder to query the fault code, and then repair according to the fault code, finally clear the fault code. However, if the failure of the repair cannot be excluded, some maintenance personnel feel that there is no way to the next step. In fact, some fault codes of electronically controlled vehicles may be poor performance in the component itself, or may be circuit disconnects or short circuits, which may also be caused by other sensors failures or interfering signals, using oscilloscope to diagnose these suspects or difficult failures. The effect is very good. The oscilloscope can display the change relationship between the measured voltage and time in real time in real time, and widely used in automotive diagnosis. Now the weight of automotive maintenance is diagnosis, so that you can understand the car diagnosis: "Diagnosis" is to obtain useful data through "hope, smell, ask, cut, sniff" or use multiple test equipment or instruments, this process is capable Accurately analyze the causes of the fault and find the premise and foundation of the fault location, however, if the test instrument or device is not displayed, some of the domestic car decoders displays the fake ignition waveform and false data stream, then the correct diagnosis result is not This wood, passive water. In addition, "break" is the analysis judgment. On the basis of the correct test data of the previous "diagnosis", the correct thinking is obtained. Technology area
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