Symptom: 05 annual output of Toyota Vios car dashboard engine failure warning lights are bright, and fuel consumption is too high. Before the speed of 20km / h or more, the four doors will automatically lock, but now when the speed reaches 20km / h or more, 4 doors will not automatically lock.
    Troubleshooting: first connected to the Toyota-specific detector to retrieve the engine fault code, fault code P0500, meaning the speed sensor circuit failure. The customer reflects that the car has ever replaced the vehicle speed sensor, but did not troubleshoot the problem. Before proceeding with the maintenance work, we should be aware of the work of the Vistage car speed sensor. The speed sensor is mounted on the transmission, and the transmission output shaft is rotated by the rotor shaft of the speed sensor driven by the driven gear. When the rotor shaft rotates, the pulse signal is generated. The pulse signal enters the combination meter and is converted into the actual speed. In addition, the waveform shaping circuit in the combination instrument can change the pulse signal inputted by the vehicle speed sensor into a more accurate square wave, and then output the square wave to the engine control unit. The engine control unit refers to this signal to select the optimum fuel injection. The square wave signal of the combined instrument is also output to the anti-theft system control unit. The anti-theft system control unit locks the four doors according to the signal when the vehicle speed exceeds 20km / h.
    According to the above work of the vehicle speed sensor, combined with the fault code P0500, you can determine the fault point may be in the vehicle speed sensor, the combination of instruments, engine control unit and the relevant wiring harness. Clear the fault code after the road test, through the detector to read the engine dynamic data flow, focusing on observation speed, I found that the data flow speed value is always 0km / h. Observe the speed of the instrument on the display, the instrument shows the speed and actual speed consistent. During the test, the engine fault warning light is lit, when the instrument shows the speed of more than 20km / h, 4 doors will not automatically lock. Retrieve the fault code, still P0500.
    Based on the above information, the vehicle shows the normal speed of the instrument, indicating that the speed sensor, instrument and speed sensor and instrument line connection between the no problem. In addition to the speed of the data in the engine control unit, other data items are normal, indicating that the engine control unit is basically no problem, the next step need to focus on checking the instrument and the engine control unit between the line connection.