Q: What is the purpose and function of the Vehicle Speed Sensor (VSS) on Chevrolet Trailblazer?
A: The Vehicle Speed Sensor (VSS) is a permanent magnet generator mounted on the transmission. It is triggered by a toothed rotor on the transmission output shaft. As the output shaft rotates, the sensor produces an AC voltage, the frequency of which is proportional to vehicle speed. The PCM uses the sensor input signal for several different engine, transmission and radio control functions. The VSS signal also drives the speedometer on the instrument panel. A defective VSS can cause various driveability and transmission problems. To replace it, raise the vehicle and support it securely on jackstands. Disconnect the electrical connector from the VSS. Remove the mounting bolt and withdraw the VSS from the transmission case. Replace the sensor O-ring and lubricate it with clean transmission fluid. Installation is the reverse of removal.