How to Replace the Speed Sensor on a GMC Vehicleby Lee Sallings
The speed sensor in your GMC vehicle provides a signal to the on-board computer that is used to calculate the speed of the output shaft of the transmission. The computer uses this signal along with the known diameter of the tire and the final drive-gear ratio to determine vehicle speed and operate the speedometer, ABS and torque-converter clutch. A faulty speed sensor can cause the ABS system to malfunction, intermittent torque-converter clutch operation, and an inoperative speedometer.
Place wheel chocks behind the passenger-side tires. Raise the driver-side of the truck with a floor jack, and slide jack stands under the frame.
Slide under the truck and locate the speed sensor on the tail-shaft housing of the transmission. Unplug the electrical connector on the sensor. Remove the 10 mm bolt that attaches the sensor to the transmission. Twist the sensor as you pull it from the transmission.
Push the new sensor carefully into the transmission tail-shaft housing. Twist and push until the sensor seats fully into the housing. Install the 10 mm bolt and plug the electrical connector into the new sensor.
Raise the truck off the jack stands and remove the stands. Lower the truck slowly to the ground.
On GMC models made before 1996, disconnect the battery to clear all the trouble codes stored in the computer. On vehicles made after 1996, clear the codes using an automotive scan tool. Test-drive the truck to verify the repair.