In theory, electric digital speedometers should have many advantages over their analog counterparts -- they're easier to read, sharper and more accurate, giving an exact number rather than a vague needle-point. Yet if your digital speedometer is malfunctioning, you are unlikely to appreciate any of these advantages. Thankfully, from checking the wiring to having certain sensors replaced, there are steps you can take to remedy any problems.
Switch your engine off and use a small screwdriver (although the method with which your digital speedometer is attached may vary depending on your vehicle) to remove the screws holding your speedometer panel in place. Gently remove the panel and visually inspect the wiring behind the panel for any loose connections.
Replace the speedometer cable -- the main cable running from the back of the speedometer -- if it is damaged. Otherwise just make sure it is securely in place. The speedometer will not function without it being in working order.
Examine the particular fault with the speedometer in order to give you a better idea what the cause of the problems is. Erratic behavior from your speedometer, such as the speed randomly changing from low to high or vice-versa. Have the speed sensor repaired or replaced in order to resolve your problem.
Check your tire size. Even something as simple as having tires fitted to your car that are not the size recommended by the manufacturer can throw the speedometer calibration out of sync. Check that your tires are the size recommended in the car's manual.
