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Emission Control Systems > < Diagram Information and Instructions|Page 3327
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Vehicle Speed Sensor: Description and Operation

VEHICLE SPEED SENSOR

DESCRIPTION 

The Vehicle Speed Sensor (VSS) consists of a reed switch built into the speedometer head. As the speedometer cable turns, the reed switch closes
the circuit ground four times per revolution. 

OPERATION

As vehicle speed increases, the frequency of ground pulses received by the ECM also increases. Therefore, by calculating the frequency of the
ground pulses, the ECM is capable of determining vehicle speed.

Emission Control Systems > < Diagram Information and Instructions|Page 3327