Knowing the appropriate speed at which to drive is important to all drivers from both a safety and practicality standpoint. A non-functioning speedometer increases the risk that you either drive too slow or too fast, potentially increasing the chance of an accident or citation from a police officer. A functioning speedometer is essential for safe driving and if you notice yours is not working properly, you should have it checked by a mechanic.
How this system works:
Your vehicle’s speedometer calculates the speed of the vehicle through interaction with the transmission and driveshaft. Your car’s computer is able to translate the rotational speed of the driveshaft into the linear speed of your vehicle, transmitted to you, the driver, through the speedometer. A speedometer that is not working fails to translate this information and can be a potential risk to drivers.
Common reasons for this to happen:
Broken Speed Sensor: A speed sensor has many purposes including indicating the speed of the vehicle, regulating flow of fuel and ignition timing, and operating the cruise control. A speed sensor that has failed may stop the speedometer from working. You may also notice that your vehicle is not running smoothly and you are not able to use the vehicle’s cruise control. When speed sensors fail, they will typically cause the Check Engine light to come on, indicating that there is an issue.
Faulty Fuse/Bad Wiring: In very wet conditions, it is possible for exposed wires to get wet and short out, causing a fuse to blow. When the fuse for your speedometer stops working, it can cause the speedometer to drop to zero.
Malfunctioning ECU: The engine control unit (ECU) acts as the vehicle’s computerized brain, monitoring many different facets of vehicle activity, including speed. If there is a problem with the ECU, it may affect the vehicle’s ability to identify what speed it is traveling at and the speedometer will drop to zero.
What to expect:
A top-rated mobile mechanic will come to your home or office to determine the reason your vehicle’s speedometer has stopped working. The mechanic will then provide a detailed inspection report outlining the reason the speedometer stopped and the cost of any repairs that need to be made.
How it's done:
A mechanic will first examine the vehicle using a code reader/scanner to review any error codes or Check Engine light the vehicle may have produced. By connecting to the vehicle’s ECU, the mechanic can get a better idea of what components may have failed.
If the mechanic believes that the speed sensor has failed, he or she will get underneath the vehicle to find the exact location of the sensor. While under the vehicle, the mechanic will examine both the sensor itself and the corresponding wires for any superficial damage to the unit. The mechanic will then remove the old speed sensor and install the new one.
If the mechanic believes that a fuse or bad wire has caused the speedometer to stop working, he or she will begin by examining the fuse to check if it has been blown. If so, the mechanic will replace the fuse. The mechanic will also examine the wires running from the speedometer to the speed sensor to see if they have been damaged in any way.
In the case of a problem with the ECU, the mechanic will typically replace the entire ECU. Because resetting the unit may just be a temporary fix, replacing the ECU is the only way to ensure that it works properly. When the mechanic installs the new ECU, he or she will turn the ignition key to the “Auxiliary” position. This will allow the new ECU to turn on and begin the process of managing vehicle systems. When the vehicle is turned on, it should be begin adjusting systems to run optimally.
In all repairs, a mechanic will clear any trouble codes that may have been produced by the vehicle’s ECU using a code reader/scanner. Before leaving, the mechanic will test drive the vehicle to ensure that all systems are working properly and the speedometer has resumed functionality.
How important is this service?
A vehicle with a speedometer that doesn’t work can be very unsafe as well as unpractical. By not knowing your speed, you may put yourself at increased risk for citation by police officers. Being unable to determine speed could also increase the potential for an accident. You should stop driving a vehicle with a non-functioning speedometer until it can be checked by a mechanic.