Vehicle Speed Sensor: Description and Operation

Vehicle Speed Sensor
The Vehicle Speed Sensor (VSS) is a magnetic inductive pickup that relays vehicle speed information to the PCM. The PCM uses this information in order to control shift timing, line pressure, and TCC apply and release.

The VSS mounts in the case extension at the vehicle speed sensor reluctor wheel, which is pressed onto the final drive carrier assembly. An air gap of 0.27 - 1.57 mm (0.011 - 0.062 inch) occurs between the sensor and the teeth on the vehicle speed sensor reluctor wheel as the final drive carrier assembly rotates.

The sensor consists of a permanent magnet surrounded by a coil of wire. As the vehicle speed sensor reluctor wheel on the final drive carrier assembly rotates, an AC signal is produced by the VSS. This AC signal consists of a voltage and frequency that changes based on vehicle speed. The PCM uses the frequency portion of this signal to determine vehicle speed. Higher vehicle speeds induce a higher frequency and a higher voltage measurement at the sensor. The voltage portion of the signal is used in diagnostic procedures.

Sensor resistance should measure between 1,650 - 2,200 ohms at 20°C (68°F). Output voltage will vary with vehicle speed from a minimum of 0.5 volts AC at 100 RPM to 200 volts at 6,000 RPM.