Cutlass V6-191 3.1L VIN M SFI (1998)
Transmission Speed Sensor: Description and Operation
VEHICLE SPEED SENSOR
The Vehicle Speed Sensor (VSS) 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 vehicle speed sensor mounts in the case as 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 vehicle speed sensor. 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.
AUTOMATIC TRANSMISSION INPUT (SHAFT) SPEED SENSOR
The Automatic Transmission Input (Shaft) Speed (A/T ISS)sensor 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 vehicle speed sensor 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 A/T ISS sensor. Higher vehicle 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.
