The most likely reason a speedometer stops working is a broken gear. Finding the problem involves removing the speedometer assembly from the vehicle and locating the problem piece. Replacements are available at dealerships, auto parts stores and online.
If the problem exists on a 2003 to 2007 GM vehicle, a faulty stepper motor is the likely cause of failure. GM's entire production line from these years uses the XC5.168 motor. There is a potential for the manufacturer to make repairs at no cost to the owner. While GM does not admit a problem with speedometers, a class action suit from 2007 requires the company to pay for repairs on certain models. The case alleges symptoms that include incorrect speedometer displays, nonworking speedometers and failure of the entire instrument panel.
Speedometer problems lead to dangerous driving issues. Drivers who are unaware of their driving speed often exceed the speed limits, a common cause of accidents. The lack of a proper functioning speedometer increases the likelihood of a speeding citation.
Issues with speedometers and their associated odometers affect new vehicle warranties. A 2007 lawsuit against Honda indicated the company's odometers read up to 3.75 percent fast. The settlement in the suit includes an extension of the manufacturer's drive-train warranty for owners of these vehicles.