Your vehicle's speed sensor has multiple purposes. It sends signals to the speedometer that indicate how fast your vehicle is travelling, it regulates the flow of fuel and ignition timing and it operates cruise control. Because the speed sensor affects the performance of several other systems on your vehicle, various signs may indicate it is not working.
The most noticeable sign of a bad speed sensor is a speedometer or odometer that stops working. Also, you may not be able to set your vehicle to cruise control.
Hesitation, roughness or sporadic jumps in your vehicle's transmission when you try to shift gears indicates your speed sensor may be the problem.
Your vehicle may rumble or idle irregularly when you start it, or it may burn more fuel than normal. Also, your vehicle may lose power suddenly due to wrong signals sent from the speed sensor to the fuel system.