Automatic Transmission Output Speed (A/T OSS) Sensor (42)
The A/T OSS sensor is a variable reluctance magnetic pickup located in the rear of the transmission case. The sensor is mounted in the case (24) opposite the rear internal gear (560). The rear internal gear is splined to the output shaft assembly (562). The sensor consists of a permanent magnet surrounded by a coil of wire. As the output shaft and rear internal gear rotate, an alternate current (AC) is induced in the coil by the 'teeth' on the rear internal gear as they pass by the magnetic pickup. Therefore, whenever the vehicle is moving, the A/T OSS sensor produces an AC voltage signal proportional to vehicle speed.
At the TCM, the AC signal is electronically converted to a 5 volt square wave pattern. The square wave pattern 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 a representation of the rear internal gear teeth. Therefore, the more teeth or waves that pass by the magnetic pickup in a given time frame, the faster the vehicle is moving. The square wave pattern is compared to a fixed clock signal internal to the TCM to determine transmission output speed.