Investigating Factors That Effect Speedometer Problems

The speedometer is a very critical part of your vehicle’s electrical system. The speedometer is how you monitor how fast or slow you are going, and therefore helps you operate as a safer, more responsible driver, as well as avoid costly speeding tickets. By law, it has to be accurate to within 1.5 mph higher or lower than the actual speed. It is operated by speed sensors in the computer system. Sometimes your speedometer will malfunction for a variety of reasons, and having it checked for accuracy periodically is a good practice to follow. Speedometers also let you know how many miles to the gallon you are receiving.

Ways to Check

You can check if your speedometer is working properly by grabbing a friend and heading out to a highway. Drive exactly one mile and use your vehicle’s cruise control feature. Drive 60 mph and have your friend use a stopwatch to see if the speedometer correlates with the stopwatch. There are also GPS devices and apps for certain phones that have a speedometer checking feature. You can also take your car into a mechanic for a full diagnostic test to determine if the speedometer is providing an accurate reading.


There are certain factors that can cause your speedometer to malfunction. If you have changed the tires on your vehicle, you may have changed the tire rolling diameter, which can affect the speedometer reading. The speedometer would need to be re-calibrated for the new size tires.

Speed Sensor

Another cause for a speedometer to not work properly is a faulty speed sensor or a dirty speed sensor. These are easy to replace should they go bad. You can change your speed sensor yourself. It is located in different places depending on whether your vehicle is a front or rear wheel drive. You can also change your speedometer cable, a black, thick wire that runs through the engine’s main body, and replace it with a new one. If replacing either of these doesn’t resolve the issue, take it to an expert who can further determine and repair the issue.


Check your battery strength. A weak battery can product an insufficient speedometer reading, so replacing an old battery, or recharging it can fix the problem.


Bad wiring can sometimes create a bouncing or moving speedometer needle. Loose wiring can also have the same affect. Visually inspect connections and make sure all your wiring is connected securely.


It’s a good idea to take your vehicle in to a professional where they can make certain the speedometer is properly calibrated. Calibration takes a very powerful electromagnet to make adjustments to the speedometer’s magnetic strength.

Being a responsible driver means controlling your speed for the safety of everyone on the road. Knowing exactly how fast or slow you are traveling is vital to prevent accidents and costly speeding tickets. Re-calibrating after a tire size change must be done so that your odometer and speedometer stay in sync. Make sure your battery is fully charged, and that your speed sensor is sending the correct information to your vehicle’s computer system. Make sure none of your wires are worn or loose. Proper vehicle maintenance at the correct time intervals is essential to making sure you and everyone around you is safe on the road.