To replace a transmission speed sensor, jack up the front of the vehicle, locate the speed sensor, remove the electrical plug, remove the speed sensor and replace with a new sensor. A faulty speed sensor causes the speedometer not to work.
Start by lifting the front of the car using a jack, placing the jack along the front frame, behind the radiator. Place a jack stand on each end of the vehicle to make it safer to work under.
Next, locate the speed sensor, usually located on the bottom of the transmission. The sensor looks like a small plug sticking out of the transmission with an attached electrical cord. Remove the connecting electrical cord from the speed sensor by clasping both ends of the cord and pulling. Remove the speed sensor by gently twisting it in a clockwise direction using a wrench.
Clean the sensor housing using a clean rug to get dirt and other debris from the threads. Insert the new speed sensor into the housing, and tighten by hand. Ensure that the new sensor is straight before tightening with a wrench. Wipe the end of the electrical cord using a rag to ensure a good connection. Reattach the cord to the sensor by pressing gently until it clicks into place.