Vehicle Speed Sensor: Operation
WARNING: This page is about a different car, the 2004 Subaru Forester. However, it is still accessible from the selected car via links, so may be relevant.
As the driven key rotates, the magnet turns causing the magnetic field of the Hall IC to change.
The Hall IC generates a signal that corresponds to a change in the magnetic field.
One turn of the driven key in the speed sensor sends 4 pulses to the combination meter, engine control module and cruise control module.