Output Speed Sensor (OSS)

WARNING: This page is about a different car, the 2004 Pontiac Sunfire and 2004 Chevrolet Cavalier. However, it is still accessible from the selected car via links, so may be relevant.

The automatic transmission output speed sensor (OSS) is a magnetic inductive pickup that relays information relative to vehicle speed to the powertrain control module (PCM). Vehicle speed information is used by the PCM to control shift timing, line pressure, and torque converter clutch (TCC) apply and release.

The 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 in) 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 OSS. Higher vehicle speeds induce a higher frequency and voltage measurement at the sensor.

Sensor resistance should be 1500-1750 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.

Fig 1: Output Speed Sensor (OSS)

Courtesy of GENERAL MOTORS CORP.