Why does the speedometer fluctuate up and down?
2 Answers
The reason for the speedometer fluctuating up and down is: a malfunction in the vehicle speed sensor. A faulty vehicle speed sensor can also cause unstable engine idling, momentary stalling or engine shutdown when starting the vehicle or decelerating to stop while driving, and reduced engine acceleration performance. The vehicle speed sensor is typically installed in the drive axle housing or transmission housing, displaying the vehicle's speed through pointer movement or generating alternating current signals. It usually consists of a magnetic core with two terminals and a coil. The output signal of the vehicle speed sensor can be a magnetoelectric AC signal, a Hall-effect digital signal, or a photoelectric digital signal.
Having driven for several years, I've noticed that when the speedometer fluctuates up and down, the issue may stem from a loose or dirty speed sensor. The sensor is located near the wheels and can easily shift or accumulate dust over time due to bumps, causing intermittent signals to reach the dashboard. Additionally, aging wiring with poor contact is another major cause, especially noticeable during rainy or humid conditions. Last time I checked it myself, I first opened the hood, located the sensor, gently cleaned it with a soft brush, and then used a multimeter to test if the voltage was stable. If the problem persists, it's crucial to visit a repair shop immediately for diagnosis to avoid accidents on the highway. Remember to have technicians inspect these components during regular maintenance—spending a little money for safety now can prevent endless troubles later. In short, don't delay; driving without knowing your actual speed is dangerous. A friend of mine once rear-ended another car because of this, so now I make it a habit to visually inspect these parts every month.
