A transmission speed sensor is an important component of the vehicle. Its implementation is for the calculation of actual gear ration, especially during the use. A vehicle mainly contains two speed sensors that work in conjunction. Defective cruise control, sluggish shifting, illuminated check engine light- are the symptoms of a malfunctioning transmission speed sensor. When you find these symptoms, take your car to a trusted car mechanic, else the wedged speed sensor can make your vehicle less efficient and leave you with a dangerous drive.