English 
speedometer bouncing up and down
1. The sudden fluctuation of the speedometer is caused by the failure of the vehicle speed sensor, which will also lead to the unstable idle speed of the engine, the instantaneous stop or shutdown of the vehicle when it starts or decelerates, and the deterioration of the acceleration performance of the engine.
2. Speedometer is the general name of vehicle odometer, which is composed of the driving speed of motor vehicles and the mileage measurement that records the driving distance of vehicles.
3. The vehicle speed sensor is usually installed in the drive axle housing or transmission housing. It displays the vehicle speed or generates an AC signal by swinging the pointer. It is usually composed of a magnetic core and a coil with two terminals.
4. The output signal of the vehicle speed sensor may be a magnetoelectric AC signal, a Hall digital signal or an optoelectronic digital signal.The vehicle speed sensor is a device used to detect the vehicle speed of an electronically controlled vehicle. The control computer uses this input signal to control engine idling, automatic transmission torque converter locking, automatic transmission shifting, engine cooling fan opening and closing, cruise and other functions.The output signal of the speed sensor can be a magnetoelectric AC signal, a hall type digital signal or a photoelectric digital signal. The speed sensor is usually installed in the drive axle housing or the transmission housing, and the signal line of the speed sensor is usually installed in the shielded jacket, which is to eliminate the electromagnetic and radio-frequency interference generated by the high-voltage electric wire, the car phone or other electronic equipment.
There is a problem with the throttle valve.The throttle valve failure may be the throttle position sensor failure or the throttle control motor failure. As the name implies, the throttle position sensor can detect the throttle opening and adjust fuel injection.The function of the throttle control motor is to open the throttle at a certain angle according to the depth of the throttle.If both components fail, the intake air of the engine will change, causing the speedometer to jump up and down when the vehicle is running. Fault of positive crankcase ventilation valve or carbon canister solenoid valve.PCV valve, i.e. positive crankcase ventilation valve, is used to return the combustible mixture blown into the cylinder to the inhaler for combustion. The carbon canister solenoid valve is used to burn gasoline from the fuel tank to the intake cylinder, thus reducing fuel consumption.If both valves fail, the fuel burned in the cylinder will leave the ECU device and the tachometer will jump up and down.
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