Electra Park Avenue V6-231 3.8L VIN 3 FI (1988)
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 Vehicle Speed Sensor (VSS) 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. The vehicle speed sensor (VSS) is located on the transmission. The VSS is a permanent magnet generator consisting of a field coil and permanent
magnet stator that produces AC voltage. When the vehicle is in motion an impulse is sent to the vehicle speed buffer. The information is then sent to the
speedometer, engine control module, cruise control module, and passive restraint module at a rate of 4004 or 2002 pulses per minute.
