Transmission Speed Sensor: Description and Operation

Vehicle Speed Sensor

4T40-E/4T45-E

The Automatic Transmission Output (Shaft) Speed Sensor (AT 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 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.





Automatic Transmission Input (Shaft) Speed Sensor

4T40-E/4T45-E

The Automatic Transmission Input (Shaft) Speed Sensor (AT ISS) is a magnetic inductive pickup that relays information about the transmission input speed to the Powertrain Control Module (PCM). The PCM uses this information to control the line pressure, Torque Converter Clutch (TCC) apply and release, and the transmission shift patterns. This information is also used to calculate the appropriate operating gear ratios and TCC slippage.
The AT ISS mounts on the transmission case under the channel plate next to the drive sprocket. An air gap of 0.26-2.90 mm (0.010-0.114 inch) is maintained between the sensor and the teeth of the drive sprocket. The sensor consists of a permanent magnet surrounded by a coil of wire. As the drive sprocket is driven by the turbine shaft, an AC signal is induced in the AT ISS. Higher engine speeds induce a higher frequency and voltage measurement at the sensor.
Sensor resistance should be 625-725 ohms when measured at 20° C (68° F). Output voltage will vary with speed from a minimum of 0.5 volts AC at 550 RPM, to 200 volts AC at 7000 RPM.