Vehicle Speed Sensor: Description and Operation

Vehicle Speed Sensor (VSS) Typical:

LOCATION

The Vehicle Speed Sensor (VSS) is located in the extension housing of the transmission (2WD), or the extension housing of the transfer case (4WD).


PURPOSE

The Vehicle Speed Sensor (VSS) is used to inform engine controller of vehicle deceleration and engine idle. The engine controller uses this information to control Idle Speed Control (ISC) motor position during these conditions.

engine controller 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 engine controller actuates Idle Speed Control (ISC) motor to maintain desired Manifold Absolute Pressure (MAP) sensor value.

During idle, engine controller actuates the ISC motor to maintain desired engine idle speed.



OPERATION

The VSS has a set of contacts inside that are opened and closed by a rotating 8 pole permanent magnet. As the magnet rotates, the magnetic field opens and closes the contacts 8 times per revolution, or 8000 times per mile.

The engine controller sends a 8 volt signal to the VSS. If the sensors contacts are open, the voltage stays at 8 volts. If the contacts are closed, the voltage will drop to 0 volts.