Circuit Description

WARNING: This page is about a different car, the 2007 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.

Vehicle speed information is provided to the engine control module (ECM) by the vehicle speed sensor (VSS). The Hall-Effect sensor contains a permanent magnet and a semiconductor plate to which ignition voltage is applied. As the output shaft spins, the rotor directs the field of the permanent magnet either toward or away from the plate. When the ignition is ON and the magnetic field is directed away from the plate, electrons are evenly distributed across the plate. When the rotor directs the field toward the plate, the electrons are redistributed unevenly across the front and back of the plate. The uneven distribution causes a voltage to be produced across the plate. The VSS produces a frequency signal that is proportional to vehicle speed. The ECM converts the VSS signal to vehicle speed, displayed on the scan tool in miles per hour and kilometers per hour. The ECM also uses the VSS signal to generate the 4,000 pulses per mile vehicle speed signal used by the instrument cluster.

When the ECM detects a very low vehicle speed, while the vehicle is in motion, DTC P0502 sets. DTC P0502 is a type B DTC.