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2003 chevy trailblazer speedometer not working
Because of the ABS. Through actual measurement, it is found that the signals output to the two control units are 5v square waves with the same number of pulses as the actual output, while the signals output to the odometer are frequency divided square waves. In the data, it is called the vehicle speed sensor calibration processing module. It is found by measuring with an oscilloscope that the output signal amplitude of the vehicle speed sensor does not increase with the increase of the vehicle speed, and the output signal amplitude is lower than the general signal.
It is suspected that the sensor is damaged. When the vehicle speed is lower than 80km/h, the three output signals are regular square waves. When the vehicle speed exceeds 80km/h, the square waves become irregular and the frequency decreases, and then a high level is directly formed without waveform. Through measurement, it is found that when the signal received by the speedometer reaches 130Hz, the vehicle speed is expressed to the maximum speed of 180km/h. When the pointer of the speedometer is at a non-zero position, if the speedometer is powered off, it will return to zero again. That is, the pointer of the speedometer rotates in the opposite direction for about 30s, after which the input speed signal can be normally indicated. This model is rare in our local market, so it is difficult to find the speed sensor in the market. Even if it is found, the price is expensive. Therefore, an old crankshaft position sensor was successfully replaced by measuring the diameter difference between the two sensors, and then a suitable bushing was processed on the lathe to make the modified sensor fit into the mounting hole, and the thickness of the nylon sleeve edge was processed, When the gap between it and the signal wheel is about 1mm, the output waveform can be correctly identified by the processing module. After the oscilloscope detection, the signal amplitude of the sensor output is significantly increased in the cold state, and the instrument can work normally at this time. The instrument shall be installed and then tested for troubleshooting.
If the vehicle speed sensor and sensor drive mechanism fail, the speedometer will not move. Check the sensor and replace it if it cannot be used. The fault of the speedometer will also cause it to stop moving. You can check the circuit. If there is a problem with the circuit, repair it in time to solve the problem. If the wire speed or mechanism between the sensor and the speedometer fails, the speedometer will also stop moving. Also, check the sensor and the speedometer to see which problem is. If it needs to be replaced, replace it in time.
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