What is the VSS on a transmission?
The vehicle speed sensor (VSS) is also commonly referred to as a transmission speed sensor or output shaft speed sensor. It is a small device—typically mounted somewhere on the transmission—that determines how fast your vehicle is going by measuring the rotation of a toothed wheel on a shaft inside the transmission. via
Can a transmission speed sensor cause limp mode?
Yes, a defective wheel speed sensor can cause limp mode in a car. A bad wheel speed sensor can result in a loss of traction control and stability. via
What are all the sensors on the transmission? (video)