Vehicle Speed Sensor: Description and Operation

Vehicle Speed Sensor
The Automatic Transmission Output (Shaft) Speed Sensor (AT OSS) is a magnetic inductive pickup that relays information relative to vehicle speed to the PCM. Vehicle speed information is used by the PCM to control shift timing, line pressure, and TCC apply and release. The AT OSS mounts in the case at the speed sensor rotor which is pressed onto the differential. An air gap of 0.27 - 1.57 mm (0.011 - 0.062 inch) is maintained between the sensor and the teeth on the speed sensor rotor. The sensor consists of a permanent magnet surrounded by a coil of wire. As the differential rotates, an AC signal is induced in the AT OSS. Higher vehicle speeds induce a higher frequency and voltage measurement at the sensor.

Sensor resistance should be 1500 - 1650 ohms when measured at 20°C (68°F). Output voltage will vary with speed from a minimum of 0.5 volts AC at 25 RPM to 200 volts AC at 1728 RPM.