Passport 2WD L4-2559cc 2.6L SOHC (4ZE1) (1994)
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Vehicle Speed Sensor: Description and Operation
General Descripion
PURPOSE
The Vehicle Speed Sensor (VSS), sends a pulsing voltage signal to the Engine Control Module (ECM), which the ECM converts to miles per
hour. This Sensor helps to control the operation of the Idle Air Control System. The number of pulses generated is four pulses per one rotation of
the Pinion Shaft.
OPERATION
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The Vehicle Speed Sensor generates a signal which indicates the Vehicle speed to the Engine Control Module (ECM).
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The Vehicle Speed Sensor is mounted on the back of the Speedometer. The Speedometer Cable rotates a magnet which closes the contacts of a
reed switch as it rotates. The reed switch contacts close and open four times for each revolution of the Speedometer Cable.
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Each time the reed switch closes, the Vehicle speed inputs are grounded by the reed switch. When the reed switch is open, input from the Engine
Control Module is held at 12 volts by voltage through a pull-up resistor in the ECM.
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When the Vehicle is moving, the ECM receives a series of voltage pulses. The rate at which the pulses are received indicates the Vehicle speed.
