Vehicle Speed Sensor: Description and Operation

Vehicle Speed Sensor (VSS) Typical:

Vehicle Speed Sensor (typical):

PURPOSE
The Vehicle Speed Sensor (VSS) located in the transfer case, is used to inform Powertrain Control Module (PCM) of vehicle deceleration and engine idle. The PCM uses this information to control Idle Air Control (IAC) motor position during these conditions.

PCM uses sensor input with input from Throttle Position Sensor (TPS) and VSS to differentiate between closed throttle deceleration or closed throttle idle.

During closed throttle deceleration, the PCM actuates IAC motor to maintain desired Manifold Absolute Pressure (MAP) sensor value.

During idle, PCM actuates the IAC motor to maintain desired engine idle speed.

VSS Circuit:

OPERATION
Theory of operation: The vehicle speed sensor is a hall-effect type sensor used to detect the vehicle speed. The PCM calculates the vehicle speed based on the VSS signal. The PCM supplies 8 volts from cavity 7 to power up the sensor. Sensor ground is supplied by PCM cavity 4. The PCM also supplies a 5.0 volt pull up voltage to the sensor from cavity 47. The VSS signal is created when the sensor alternates the 5.0 volt pull up from high to low.