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Link: lemon-manuals.la or lemon-manuals.org.ua

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Vehicle Speed Sensor: Description and Operation

DESCRIPTION
The Vehicle Speed Sensor (VSS) consists of a reed switch built into the speedometer head. As the magnet turns with the speedometer cable, its magnetic field causes the reed switch to turn "ON" and "OFF."

OPERATION
The "ON," "OFF" frequency increases or decreases in proportion with the vehicle speed and is sent to the ECM as a digital signal.