Eldorado V8-350 5.7L DSL (1984)
Vehicle Speed Sensor: Description and Operation
1982-84 Models with DEFI
The speed sensor consists of a LED (light emitting diode) and a photo transistor enclosed in a housing which connects to the rear of the speedometer
cluster. The photo transistor generates an electrical signal corresponding to vehicle speed when it is exposed to light from the LED, which is reflected off
each passing bar of the rotating speedometer drive magnet into the photo transistor.
The speed sensor produces a weak voltage signal and must be used for several speed inputs, therefore, a buffer amplifier is positioned between the
speed sensor and the ECM to amplify and distribute the speed signal, and invert this speed signal into a format which can be understood by the ECM.
1982-84 Models Except DEFI
The speed sensor operation is similar to the DEFI, except the speed signal is transmitted to an electronic controller. On diesel equipped vehicles with
digital speedometer cluster, the speed sensor circuit is the same as used on non-DEFI models; however, diesel equipped vehicles with mechanical
speedometer cluster do not use a buffer amplifier in their speed sensor circuit.
