While driving, it's important to know how fast you're going. All modern vehicles are (and legally have to be) installed with a speedometer--a gauge that provides an instantaneous reading of its speed. While they might vary by their layout, level of technology, and the type of display, they will all serve this necessary function. If yours is not working well, such as displaying the wrong reading, it's important that you get it repaired or replaced as soon as possible. Keep reading on to learn more about the different types of speedometers, how they work, and what to do if you suspect yours is faulty.

Types of Speedometers in Cars

Analog

The analog type is the traditional speedometer that makes use of hands and dials to give you real-time readings of your vehicle's speed. With analog speedometers, changes in speed are more visible as the dial moves physically. However, parallax errors can result in less than precise readings.

Digital

Many modern vehicles have digital speedometers that show the speed on a digital display. These are easier to read, are usually more accurate, and aren't affected as much by wear and tear as the analog types.

How the Speedometer Works

In older eddy-current speedometers, the vehicle's transmission output shaft drives a flexible speedometer cable, which then spins a magnet inside the speedometer assembly to generate eddy currents and move the needle, indicating speed. The cable spins a magnet to create eddy currents in the speed cup and make it turn, and consequently, the pointer on the dial is turned to indicate the speed.

Modern vehicles use electronic sensors (Vehicle Speed Sensors) in the transmission, which send signals to the ECU, allowing digital or analog displays to show speed.

How to Choose a Speedometer

Vehicle Compatibility

To guarantee a proper fit and the original level of performance, ensure that you're getting a speedometer specific to your vehicle, as they can differ between models and even model years.

Aftermarket or OEM

Original Equipment Manufacturer (OEM) speedometers are typically made by authorized manufacturers, whereas aftermarket speedometers are made by third-party manufacturers.

We recommend investing in OEM speedometers to return your vehicle to its original level of performance. Because of the more stringent levels of manufacturing, you'll likely get more use out of an OEM replacement. Not to mention, aftermarket units may void your vehicle's warranty.

Symptoms of a Failing Speedometer

If your vehicle or the speedometer is exhibiting any of these signs, you should get the speedometer checked out.

Completely Stops Working

A sure sign of a faulty speedometer or related parts is when it completely stops working.

Check Engine Light Comes On

If the "Check engine" light comes on, you might also want to get your speedometer checked out.

Frequent Changes in the Readings

If the reading of your speedometer frequently changes when it's not supposed to, you should have it tested by an automobile professional.

Reasons Your Speedometer is Not Working

The above symptoms can be due to a number of issues, such as a bad speed sensor, ECU problems, or defective wiring.

Bad Speed Sensor

If the speed sensor is faulty, it won't be able to accurately detect the speed of the turning wheels, which will lead to inaccurate speed readings on the display. The offending sensors will likely have to be replaced.

ECU Problems

A faulty ECU can result in the fuel gauges malfunctioning. The ECU will likely have to be recalibrated with the help of automobile professionals.

Defective Wiring

Defective wiring can cause the speed sensor to malfunction and might cause the needle to quiver between speeds. The wiring will likely have to be replaced.

Routine Maintenance: Speedometer Calibration

Your speedometer must always display the correct speed. If you suspect that it isn't, or if you have just changed its tires, it might need to be calibrated. You can get this done by yourself or with the help of an automobile professional.

You will need a speedometer recalibration device to recalibrate your speedometer. Once you've gotten your hands on one, you'll need a GPS-connected device to verify speed and provide you with a percentage of error. Plug the recalibration device into the speedometer and follow the device's instructions to enter the amount of compensation needed.

Replacing Your Speedometer

DIY vs. Professional replacement--due to the complexity, professional installation is recommended.
While it is possible to replace your speedometer yourself, we recommend seeking a professional's help due to its complexity. Otherwise, if you're feeling up to the task, you can follow the following steps:
1. Disconnect your vehicle's battery to avoid electric shock
2. Loosen the screws around your vehicle's instrument cluster and pull the instrument cluster out
3. Locate the speedometer on the cluster and take a clear photo of the wiring to have an accurate reference for the configuration
4. Disconnect the wiring and speedometer
5. Install the new speedometer by doing the reverse of the preceding steps
6. Finally, test the speedometer's calibration using a GPS speed tracking app or a calibrated radar speedometer.

Where to Buy Quality Used Speedometer

At BE FORWARD Auto Parts, Japan's leading auto parts exporter, we offer a wide selection of high-quality used speedometers at competitive prices. Each speedometer is thoroughly inspected to ensure it meets our strict quality standards, providing you with a dependable part for your vehicle. Don't miss out--visit BE FORWARD Auto Parts today to secure your speedometer!