Automatic Transmission Output Speed (A/T OSS) Sensor Assembly (62)
The A/T OSS sensor is an active, hall effect pickup located in the top of the transmission case. This sensor is mounted in the case opposite the parking lock gear (253) that is splined to the front differential transfer drive gear carrier assembly (259) shaft. As the front differential transfer drive gear carrier assembly shaft and parking lock gear rotate, a square wave voltage signal is generated by the "teeth" on the parking lock gear as they pass by the pickup. Therefore, whenever the vehicle is moving, the A/T OSS sensor produces a square wave voltage signal proportional to vehicle speed. The voltage output does not depend on rotation speed. Therefore, the sensor is capable of detecting slow rotational speeds. This signal is sent to the TCM.
The square wave form can then be interpreted as transmission output speed by the TCM through the frequency of square waves in a given time frame. The square waves can be thought of as the parking lock gear teeth. Therefore, the more teeth (or waves) that pass by the pickup in a given time frame, the faster the vehicle is moving. The square wave form is compared to a fixed clock signal internally within the TCM to determine transmission output speed.