Vehicle Speed Sensor: Description and Operation

Vehicle Speed Sensor:

The Vehicle Speed Sensor (VSS) is made up of a coil, which is mounted on the transmission, and a tooth rotor which is mounted to the output shaft in the transmission. As each rotor tooth nears the coil, the coil produces an Alternating Current (AC) voltage pulse. As the vehicle speed increases, the number of AC voltage pulses increase. The Digital Ratio Adapter Controller (DRAC) processes input from the VSS sensor and output signals from the speedometer, computer, and cruise control module. The DRAC takes the voltage pulses from the VSS sensor and uses them to open and close four solid state output switches to ground at a rate proportional to vehicle speed. The DRAC is matched to the vehicle based on final drive ratio and tire size. It is important to make sure the correct DRAC module is replaced on the vehicle if replacement is necessary.