Output Speed Sensor
WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 2003 GMC Sierra, 2003 GMC Cab & Chassis Sierra, 2003 Chevrolet Silverado, 2003 Chevrolet Cab & Chassis Silverado, and 2002 GMC Sierra. However, it is still accessible from the selected car via links, so may be relevant.
On 2WD transmissions, if present, remove output speed sensor shipping cover. Remove sensor retaining bolt and remove output speed sensor from rear cover. Remove sensor "O" ring. See Figure.