4 important things to know about your car's speedometer

The car's speedometer is located on the dashboard and shows how fast the car is moving while driving. Today, speedometers are electronic and are standard on all cars.

Common problems with speedometers

Speedometers can have problems caused by the components that make up the mechanism. Sometimes speedometers don't work at all, which can be caused by a faulty speedometer head. Another problem is that the Check Engine light comes on after the speedometer stops working. This can happen when the speed sensors stop sending information to the car's computer. In this case, the speed cable may need to be replaced.

Signs that your speedometer is not working properly

Common signs that your speedometer is not working include: the speedometer is not working or acting erratically while driving, the Check Engine light comes on and off, and the overdrive light comes on and off for no reason.

Speedometer inaccuracy

The speedometer can have an error of plus or minus four percent in the United States. For lower speeds, this means that you can go faster than the speedometer indicates. For higher speeds, you can drive at least three miles per hour slower. Tires may be the cause, as under-inflated or under-inflated tires affect the speedometer reading. The speedometer is calibrated based on your vehicle's factory tires. Over time, tires on a car wear out or need to be replaced. Worn tires can make your speedometer read off, and if new tires don't fit your vehicle, they can also make your speedometer read inaccurate.

How to check speedometer accuracy

If you think your speedometer is not accurate, you can use a stopwatch to check how accurate it is. Start the watch when you pass the highway mile marker and then stop it as soon as you pass the next marker. The second hand of your stopwatch will be your speed. Another way to check accuracy is to have the car seen by a mechanic. That way, if there is a problem, they can fix it while the car is in the shop.