Impulse Hatchback L4-1809cc 1.8L DOHC (4XF1-W) (1992)
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Vehicle Speed Sensor: Description and Operation
Circuit Operation
The vehicle speed sensors generate a signal which indicates the vehicle speed to the electronic control module (ECM), the cruise control unit and the
transmission control module (TCM).
The vehicle speed sensor no. 2 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.
Each time the reed switch closes, the vehicle speed inputs are grounded by the reed switch. When the reed switch is open, the electronic control module
(ECM) input, the cruise control unit, and the transmission control module (TOM) are held at I 2 volts by voltage through a pull-up resistor in the
component.
When the vehicle is moving, the units receive a series of voltage pulses. The rate at which the pulses are received indicates the vehicle speed.
Vehicle is speed sensor no. 1 is mounted in the transaxle. It is a magnetic pick-up coil which generates an A/C voltage as a toothed exciter ring passes it.
The frequency of the generated signal is proportionate to the vehicle speed. The signal is input to the transmission control module (TOM).
