Vehicle Speed Sensor: Description and Operation

LOCATION

The vehicle speed sensor is located in the extension housing of the transmission (2WD), or the extension housing of the transfer case (4WD).


PURPOSE

Sensor is used to inform Powertrain Control Module (PCM) of vehicle speed, vehicle acceleration, or deceleration.


OPERATION

Vehicle Speed Sensor (VSS) Typical:

Sensor generates 8 voltage pulses per axle shaft revolution (sent directly to PCM).

PCM uses sensor input with input from Throttle Position Sensor (TPS) to determine closed throttle deceleration or closed throttle idle (vehicle stopped).

During idle, (no signals being received from sensor), PCM actuates Idle Air Control (IAC) motor to maintain desired engine idle speed.

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

The vehicle speed sensor input signal is also used as a mileage reference for the Service Reminder Indicator (SRI) lamp, and also to maintain speed control operation.