Analog or digital – whatever speedometer we have in our vehicle, we need it tiptop at any moment. It can save us from mishaps or give fines to the legal authority. But assume that the needle is fluctuating or there are weird readings on the display. In such situations, you may ask, “Why is my speedometer going up and down?”
Well, there are various reasons why a speedometer fluctuates. From my experience and knowledge, there can be faults with wiring, speed sensors, and instrument gauge clusters. A binding speedometer cable or a badly integrated chip can cause the issue.
Wrong readings on the speedometer can be a bit confusing and even alarming. But don’t worry, I am here to explain this issue. In this discussion, I will detail the reasons and their definitions.
A Brief to Speedometer
Definition
For sure, a speedometer is a well-known device or component of any vehicle, particularly in cars. We may also call it a speedo or gauge. Hence, this device has a mechanical connection with the gearbox output shaft (source).
According to Wikipedia, it measures and displays the rapid or instant speed at which we drive the vehicle. We need a speedo for our safety as it can help us maintain a sensible speed on the road (source). Again, we can get speed, distance, fuel level, etc., readings on the speedometer of a car, truck, or motorcycle (source).
Types of Speedometers
You can find two types of speedos: mechanical and electronic. Most modern vehicles have electronic gauges.
Mechanical speedos work by linking mechanically to the gearbox output shaft. According to Wikipedia, it operates on the “governor principle where a rotating weight moves further out” as the speed increases. Surprisingly, the device worked with a chronometric method in some old models. In those models, the distance traveled was measured over a precise time interval.
Modern speedometers have a rotation sensor mounted in the transmission. These speedos are getting popular nowadays. Still, you can trust the mechanical counterparts. Anyway, the sensor delivers a series of electronic pulses. The frequency of those pulses relates to the driveshaft’s rotational speed. Hence, it indicates the speed of a car. There is also an electronic circuit to count how quickly those pulses arrive. Then, the number gets displayed on the speedo’s LCD.
Common Reasons for Speedometer Going Up and Down (With Solutions)
Enough about the definition and types, right? But learning about them can help you understand the reasons behind speedo fluctuations. Now, I will discuss the causes of a defective speedometer or incorrect speedo readings.
Faulty Speed Sensors
The digital or electronic speedometer has a speed sensor (in short, VSS). It gives instantaneous data about vehicle speed. Vehicle speed sensor or VSS monitors the vehicle’s speed by calculating the crankshaft rotation (source).
But often, VSS can get defects that may result in fluctuations in the meter readings. It is an electrical fault that may arise due to issues with wiring or connector (source). The sensor can also get damaged or cracked, affecting its functionality.
A faulty speed sensor can affect the car’s starting system. Also, it can prevent the vehicle from starting (source).
Solutions
You need to replace the VSS to sort out the fluctuating gauge. Usually, it takes $100-$250 to replace the speedo (source). But if you want to replace it yourself, count $8-$100 for a new speed sensor.
Damaged Speedometer Cables
If you think of mechanical speedos, it has a cable to display the vehicle’s current speed. It connects the meter to the transmission. Likewise, it transmits the vehicle’s speed through a rotating cable within a protective housing. But it can be another reason why your speedometer goes up and down.
Over time, you will see these cables becoming worn, frayed, or broken. And when these things happen, the gauge stops working or fluctuating weirdly (source). The needle on the speedo will jump from one speed to another.
Solutions
You need to lubricate the cable housing. Often, the replacement of the entire cable and housing can solve the issue. Usually, you may need to spend $50-$100 to replace the car speedometer cable (source).
Malfunctioning Vehicle Computer Systems
Most modern cars have an Electronic Control Unit (ECU) or Engine Control Module (ECM). These computer systems can control many internal engine systems besides the speedometer. When the ECU or ECM malfunctions, the car may not read the speed signal from the VSS. It causes the speedometer to show fluctuating results (source).
Solutions
You can replace the ECU to solve the issue. Usually, it costs $85-$108 to replace the ECU. But you may need to pay more in certain conditions (source).
Other Reason Why Speedometer Fluctuates
Besides the above reasons, there are more to keep you in tension of dealing the defective speedometer. Mechanical failures, like worn-out small gears in the speedometer, odometer, and tachometer, can lead to fluctuations (source). Another reason can be a blown fuse connected to the gauge (source).
If your vehicle has the voltage regulator problem, it can also cause the gauge to read low or erratically (source). Again, if you have a habit of off-road driving, you can have strange speedometer readings. It’s because excessive vibration can loosen the circuit board connection (source).
How Can I Prevent My Speedometer Going Up and Down?
According to Safety Restore and Your Mechanic, you can follow these instructions to avoid fluctuating car speedometer readings.
Regular Vehicle Maintenance
Read the owner’s manual and follow the instructions. There will be suggestions or recommendations for the maintenance schedule. It may include regular inspections. Also, you should take your vehicle for servicing any electrical and mechanical systems.
I would suggest you check and maintain the speedo cable and sensors regularly. It will prevent any upcoming problems. Also, inspect the cable for any signs of wear, fraying, or damage, and replace it if necessary.
Importance of Timely Repairs
If you find any damage after inspections, you should repair or replace the affected part soon. Particularly, when you notice any inaccuracies or erratic behavior with the gauge, you should call an expert mechanic.
Regularly monitor the check engine light. It is because a defective speedo or VSS can trigger the light to come on. However, you should disconnect and reconnect the battery to reset the light if the light remains after replacing the VSS.
Keeping up with Technological Updates
As the days are advancing, we need to stay updated! Similarly, the world of modern cars is also enhancing further. In this case, you should stay informed about speedo calibration and maintenance technological updates.
The newer models of cars may have better but more critical sensors. So, you should keep an eye on trends to learn about calibration and using tools to sort the problems.
Frequently Asked Questions
Why are my car gauges jumping?
Answer: There are possible issues with car VSS (speed sensors), cables of gauge, and malfunctioning ECU. You need to inspect manually to discover the main reason.
What are the symptoms of a defective or malfunctioning speedometer?
Answer: You may see several signs like numb or bouncing needles, incorrect readings at any car pace. The gauge may also fluctuate wildly while driving at a steady speed.
Can fluctuation of speedometer affect the vehicle’s performance?
Answer: Well, it doesn’t affect the car’s performance directly. But it can invite other issues. I am giving you an example: you don’t know the actual speed. Then, possibly you are breaking the law or about to become a reason or meet road accident.
Conclusion
Still, are you thinking, “Why is my speedometer going up and down?” I hope you have the answer now. In this blog, I have tried to share all the reasons for having a defective speed gauge. Also, I have suggested possible suggestions to solve the problem.
If you liked the discussion, please leave your comments. Again, I wish you happy and safe driving with a healthy speedo!
Thank you!
