Vehicle Speed Sensor: Description and Operation

On models with conventional instrument panels, a speedometer frame mounted optic head is used to pick up light reflected by a speedometer cable mounted blade. The reflected light is produced by a light emitting diode (L.E.D.). As the speedometer cable mounted blade enters the L.E.D. light beam, the light is reflected into the optic head. From there, the light enters a photocell in the optic head and produces a low power speed signal. This signal is sent to a buffer for amplification and conditioning, then to the controller.
On models with electronic speedometers or electronic instrumentation, a transmission mounted speed sensor is used. This sensor utilizes a permanent magnet (PM) to generate vehicle speed information to the controller. Some models use a buffer amplifier to modify the sensor output.