DTC P0500: Vehicle Speed Sensor (ALLISON A/T): Description
WARNING: This page does not describe the selected car, but rather 13 other vehicles, including the 2002 GMC Yukon XL, 2002 GMC Sierra, 2002 GMC Savana Special, 2002 GMC Savana Camper Special, and 2002 GMC Savana. However, it is still accessible from the selected car via links, so may be relevant.
The Vehicle Speed Sensor (VSS) monitors the rotation speed of the transmission output shaft. The VSS assembly is a permanent magnet generator. It produces an AC voltage as the rotor teeth on the output shaft of the transmission, 2WD, or transfer case, 4WD, pass through the sensor's magnetic field. The AC voltage frequency and amplitude increase as the vehicle speed increases. The TCM will send a controlled duty cycle voltage to the Powertrain Control Module (PCM) that operates in a range of -4.5 volts to +5.0 volts. The PCM converts this signal into vehicle speed. As vehicle speed increases, the frequency of the duty cycle will increase.