Vehicle Speed Sensor Operation

The ECU expects to see a digital signal of four pulses for each speedometer cable revolution when the vehicle is moving. The vehicle speed sensor (VSS) provides this signal.

There are two different types of vehicle speed sensors used to supply information to the engine ECU. Although these sensors differ in design, the final output signal to the ECU is the same for both, four digital pulses per cable revolution.

Reed Switch Type Vehicle Speed Sensor

Reed Switch Type: The Reed Switch vehicle speed sensor is located in the combination meter assembly and is operated by the speedometer cable. The sensor consists of an electrical reed switch and a multiple pole permanent magnet. As the the speedometer cable turns, the permanent magnet rotates past the reed switch. The magnetic flux lines cause the contacts to open and close as they pass. The magnet is arranged so that the sensor contacts open and close four times for each revolution of the sensor.

Do It Yourself Car Diagnosis

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