Why does the speedometer needle fluctuate up and down?

[DeDelaney]

Speedometer needle fluctuations are usually normal as long as the amplitude isn't particularly large. How speedometers work: The speedometer consists of a permanent magnet fixed to the drive shaft, an aluminum cup with shaft and pointer, a housing, and a dial firmly attached to the casing. When not in operation, the aluminum cup, under the action of a spiral spring (hairspring), keeps the pointer at the zero position on the scale. Types of speedometers: Common vehicle speedometers are typically divided into three types: purely mechanical, electro-mechanical, and fully electronic. The purely mechanical type has basically exited the market, the electro-mechanical type is most widely used, while the fully electronic type is typically used in the bus industry.

[StevenFitz]

I've personally experienced the speedometer needle fluctuating up and down quite a few times. I remember last year when I was driving to the countryside, the speed needle on the dashboard kept jumping around, making me really nervous. Later, after inspection, it turned out the speed sensor was old and faulty, causing unstable signals. Other possible causes include loose wiring connections, dashboard malfunctions, or circuit short circuits. I tried checking the fuse box myself and found a blown fuse—replacing it fixed the issue. However, if the problem persists, don’t take it lightly; try stopping and restarting the car. Frequent occurrences can affect speed judgment and increase accident risks. It’s advisable to regularly maintain the electrical system and use professional diagnostic tools.

[VonVincent]

It's really annoying when the speedometer needle keeps flickering back and forth while driving! As an ordinary car owner, I've encountered this issue several times. It might be caused by a dirty sensor clogged with dust or poor wire contact. Once during rainy weather, water seeped into the circuit and the needle stopped working completely. It's best to first pull over and check if the fuses are intact, then gently tap the dashboard to test. Regularly prevent the vehicle's wiring from getting damp or aging. If the problem persists, visit a professional repair shop immediately to avoid sudden malfunctions on the road. Don't wait until it develops into a bigger issue that compromises driving safety.

[AubreeLee]

The speedometer fluctuates up and down, commonly due to interrupted speed sensor signals. Possible causes include loose wire connectors, aged or rusted sensors, or instrument cluster malfunctions. Check if the relevant fuse in the fuse box is blown, then ensure all wire connections are secure. If fluctuations are accompanied by other electrical abnormalities, it may indicate unstable battery power supply. Address the issue promptly to prevent misjudging vehicle speed and increasing accident risks. It's advisable to have a technician use a multimeter to test circuit impedance.