DTC P0502: Vehicle Speed Sensor Low Output (4L80-E 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 Automatic Transmission Output Shaft Speed (AT OSS) sensor, which is a permanent magnet generator, produces an AC voltage as the transmission speed sensors rotor teeth pass through the magnetic field of the sensor. The AC voltage level and the number of pulses increase as the speed of the vehicle increases. The Powertrain Control Module (PCM) converts the voltage to a digital signal for vehicle speed. The vehicle speed is used for engine and transmission calculations. If the PCM detects a low vehicle speed and there is a high engine speed in a drive gear range, DTC P0502 sets. DTC P0502 is a type "C" DTC. For California emissions and vehicles under 8,600 GVW, DTC P0502 is a type "B" DTC.