Transmission Speed Sensor: Description and Operation

Automatic Transmission Input Shaft Speed Sensor
The Automatic Transmission Input Shaft Speed Sensor (AT ISS) is a magnetic inductive pickup that relays information about the transmission input speed to the PCM. The PCM uses this information to control the line pressure, 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.